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[
"Universe",
"has quality",
"gravity"
] |
Cosmological models
Model of the universe based on general relativity
General relativity is the geometric theory of gravitation published by Albert Einstein in 1915 and the current description of gravitation in modern physics. It is the basis of current cosmological models of the universe. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations. In general relativity, the distribution of matter and energy determines the geometry of spacetime, which in turn describes the acceleration of matter. Therefore, solutions of the Einstein field equations describe the evolution of the universe. Combined with measurements of the amount, type, and distribution of matter in the universe, the equations of general relativity describe the evolution of the universe over time.With the assumption of the cosmological principle that the universe is homogeneous and isotropic everywhere, a specific solution of the field equations that describes the universe is the metric tensor called the Friedmann–Lemaître–Robertson–Walker metric,
|
has quality
| 99 |
[
"possesses quality",
"exhibits quality",
"displays quality",
"features quality",
"has characteristic"
] | null | null |
[
"Universe",
"has part(s) of the class",
"dark matter"
] |
Composition
The universe is composed almost completely of dark energy, dark matter, and ordinary matter. Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass–energy of the universe) and antimatter.The proportions of all types of matter and energy have changed over the history of the universe. The total amount of electromagnetic radiation generated within the universe has decreased by 1/2 in the past 2 billion years. Today, ordinary matter, which includes atoms, stars, galaxies, and life, accounts for only 4.9% of the contents of the Universe. The present overall density of this type of matter is very low, roughly 4.5 × 10−31 grams per cubic centimetre, corresponding to a density of the order of only one proton for every four cubic metres of volume. The nature of both dark energy and dark matter is unknown. Dark matter, a mysterious form of matter that has not yet been identified, accounts for 26.8% of the cosmic contents. Dark energy, which is the energy of empty space and is causing the expansion of the universe to accelerate, accounts for the remaining 68.3% of the contents.Dark matter
Dark matter is a hypothetical kind of matter that is invisible to the entire electromagnetic spectrum, but which accounts for most of the matter in the universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the universe. Other than neutrinos, a form of hot dark matter, dark matter has not been detected directly, making it one of the greatest mysteries in modern astrophysics. Dark matter neither emits nor absorbs light or any other electromagnetic radiation at any significant level. Dark matter is estimated to constitute 26.8% of the total mass–energy and 84.5% of the total matter in the universe.
|
has part(s) of the class
| 111 |
[
"is composed of",
"contains",
"comprises",
"consists of",
"includes"
] | null | null |
[
"Universe",
"significant event",
"photon epoch"
] |
Photons
A photon is the quantum of light and all other forms of electromagnetic radiation. It is the carrier for the electromagnetic force. The effects of this force are easily observable at the microscopic and at the macroscopic level because the photon has zero rest mass; this allows long distance interactions.: 1470 The photon epoch started after most leptons and anti-leptons were annihilated at the end of the lepton epoch, about 10 seconds after the Big Bang. Atomic nuclei were created in the process of nucleosynthesis which occurred during the first few minutes of the photon epoch. For the remainder of the photon epoch the universe contained a hot dense plasma of nuclei, electrons and photons. About 380,000 years after the Big Bang, the temperature of the Universe fell to the point where nuclei could combine with electrons to create neutral atoms. As a result, photons no longer interacted frequently with matter and the universe became transparent. The highly redshifted photons from this period form the cosmic microwave background. Tiny variations in temperature and density detectable in the CMB were the early "seeds" from which all subsequent structure formation took place.: 244–266
|
significant event
| 30 |
[
"Landmark event",
"Key happening",
"Pivotal occurrence",
"Momentous incident",
"Notable episode"
] | null | null |
[
"Universe",
"significant event",
"Lepton epoch"
] |
Leptons
A lepton is an elementary, half-integer spin particle that does not undergo strong interactions but is subject to the Pauli exclusion principle; no two leptons of the same species can be in exactly the same state at the same time. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Electrons are stable and the most common charged lepton in the universe, whereas muons and taus are unstable particles that quickly decay after being produced in high energy collisions, such as those involving cosmic rays or carried out in particle accelerators. Charged leptons can combine with other particles to form various composite particles such as atoms and positronium. The electron governs nearly all of chemistry, as it is found in atoms and is directly tied to all chemical properties. Neutrinos rarely interact with anything, and are consequently rarely observed. Neutrinos stream throughout the universe but rarely interact with normal matter.The lepton epoch was the period in the evolution of the early universe in which the leptons dominated the mass of the universe. It started roughly 1 second after the Big Bang, after the majority of hadrons and anti-hadrons annihilated each other at the end of the hadron epoch. During the lepton epoch the temperature of the universe was still high enough to create lepton–anti-lepton pairs, so leptons and anti-leptons were in thermal equilibrium. Approximately 10 seconds after the Big Bang, the temperature of the universe had fallen to the point where lepton–anti-lepton pairs were no longer created. Most leptons and anti-leptons were then eliminated in annihilation reactions, leaving a small residue of leptons. The mass of the universe was then dominated by photons as it entered the following photon epoch.
|
significant event
| 30 |
[
"Landmark event",
"Key happening",
"Pivotal occurrence",
"Momentous incident",
"Notable episode"
] | null | null |
[
"Universe",
"has part(s)",
"galaxy filament"
] |
Matter, dark matter, and dark energy are distributed homogeneously throughout the universe over length scales longer than 300 million light-years or so. However, over shorter length-scales, matter tends to clump hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, superclusters and, finally, large-scale galactic filaments. The observable universe contains as many as 200 billion galaxies and, overall, as many as an estimated 1×1024 stars (more stars than all the grains of sand on planet Earth). Typical galaxies range from dwarfs with as few as ten million (107) stars up to giants with one trillion (1012) stars. Between the larger structures are voids, which are typically 10–150 Mpc (33 million–490 million ly) in diameter. The Milky Way is in the Local Group of galaxies, which in turn is in the Laniakea Supercluster. This supercluster spans over 500 million light-years, while the Local Group spans over 10 million light-years. The Universe also has vast regions of relative emptiness; the largest known void measures 1.8 billion ly (550 Mpc) across.
|
has part(s)
| 19 |
[
"contains",
"comprises",
"includes",
"consists of",
"has components"
] | null | null |
[
"Universe",
"has part(s)",
"observable universe"
] |
Support of life
The fine-tuned universe hypothesis is the proposition that the conditions that allow the existence of observable life in the universe can only occur when certain universal fundamental physical constants lie within a very narrow range of values. According to this hypothesis, if any of several fundamental constants were only slightly different, the universe would have been unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is understood. Whether this is true, and whether that question is even logically meaningful to ask, are subjects of much debate. The proposition is discussed among philosophers, scientists, theologians, and proponents of creationism.
|
has part(s)
| 19 |
[
"contains",
"comprises",
"includes",
"consists of",
"has components"
] | null | null |
[
"Universe",
"different from",
"observable universe"
] |
Shape
General relativity describes how spacetime is curved and bent by mass and energy (gravity). The topology or geometry of the universe includes both local geometry in the observable universe and global geometry. Cosmologists often work with a given space-like slice of spacetime called the comoving coordinates. The section of spacetime which can be observed is the backward light cone, which delimits the cosmological horizon. The cosmological horizon (also called the particle horizon or the light horizon) is the maximum distance from which particles can have traveled to the observer in the age of the universe. This horizon represents the boundary between the observable and the unobservable regions of the universe. The existence, properties, and significance of a cosmological horizon depend on the particular cosmological model.
An important parameter determining the future evolution of the universe theory is the density parameter, Omega (Ω), defined as the average matter density of the universe divided by a critical value of that density. This selects one of three possible geometries depending on whether Ω is equal to, less than, or greater than 1. These are called, respectively, the flat, open and closed universes.Observations, including the Cosmic Background Explorer (COBE), Wilkinson Microwave Anisotropy Probe (WMAP), and Planck maps of the CMB, suggest that the universe is infinite in extent with a finite age, as described by the Friedmann–Lemaître–Robertson–Walker (FLRW) models. These FLRW models thus support inflationary models and the standard model of cosmology, describing a flat, homogeneous universe presently dominated by dark matter and dark energy.
|
different from
| 12 |
[
"not same as",
"not identical to",
"distinct from",
"separate from",
"unlike"
] | null | null |
[
"Time War (Doctor Who)",
"participant",
"Davros"
] |
Progression
The 'duration' and extent of the War has been unclear. The statement made by Jack Harkness in "The Parting of the Ways" – confirmed by the Doctor – that the Daleks "vanished out of time and space" to fight the War, would indicate that it was not waged in normal space-time. Nonetheless, there was fighting on the planet Gallifrey. At some point, however, the conflict engulfed a sufficient bulk of the cosmos for Cass, a character from "The Night of the Doctor", to declare that the Daleks and Time Lords had not yet succeeded in their efforts to destroy it - some of it was "still standing". Several races hostile to the Time Lords, e.g. the Sontarans, wished to participate but were forbidden to do so.The Doctor claims to have fought on the front lines and was present at the Fall of Arcadia. Arcadia was Gallifrey's second city fortified with four hundred "sky trenches". These were thought to be impregnable until an invading Dalek squadron swept them away (as seen in the 2013 mini-episode "The Last Day").The 2013 mini-episode "The Night of the Doctor" reveals that the Eighth Doctor at first was a conscientious objector, instead working to help where he could. This led him to attempt to save a woman from a spaceship crashing towards the planet Karn, who refused his aid because he was a Time Lord, apparently believing that the Time Lords had become just as destructive as the Daleks. The Doctor was killed in the crash, but was restored to life temporarily by the Sisterhood of Karn, who finally convinced him that for the sake of the universe, he had to take a stand and fight. They further offered an elixir that would control his regeneration and allow him to take a form best suited for the task. The Doctor accepted, remarking that there was no need for a Doctor in a universe consumed by war, and regenerated into the War Doctor.Davros, the creator of the Daleks, also fought during the war after his creations (which had turned against him during Genesis of the Daleks but caused his revival in Destiny of the Daleks) rehabilitated him to a leadership position. In the first year of the War, Davros' command ship was seemingly destroyed at the Gates of Elysium after flying into the jaws of the Nightmare Child. Unbeknownst to the Doctor, who had tried to save him, Davros was rescued by Dalek Caan, who had escaped the events of "Evolution of the Daleks" (2007) via an emergency temporal shift.The war resulted in countless millions dying endless deaths, as time travel was used by both sides to reverse battles that caused massive fatalities on both sides. These excesses of temporal warfare eventually led to the whole of the conflict becoming "time-locked", so that no time traveller could go back into it. The Doctor described the final days of the war as "hell", featuring "the Skaro Degradations, the Horde of Travesties, the Nightmare Child, the Could-Have-Been King with his army of Meanwhiles and Never-Weres".As the war progressed, the Time Lords became increasingly aggressive and unscrupulous. Growing in desperation, they accessed a cache of forbidden doomsday weapons fashioned by the ancients of Gallifrey known as the Omega Arsenal. All were wielded against the Dalek menace save one: "the Moment". Moreover, they resurrected the Master, a renegade Time Lord and nemesis to the Doctor, as they believed him to be the "perfect warrior for a time war". However, after the Dalek Emperor gained control of the Cruciform, the Master deserted his post, used the chameleon arch to disguise himself as a human and escaped to a time period shortly before the end of the universe. Genetically a human, he escaped the destruction of all Time Lords as well as detection by the Doctor – who was unaware of his resurrection in the first place. The Master also remained ignorant of the latter phase and outcome of the war until he emerged from hiding, when he was told by the Doctor many years later.Leadership among the Time Lords remained vague during the earlier phase of the war. Ultimately, Rassilon, founder of the Time Lord society and its time travel technology who had discovered the secret of immortality, returned to assume leadership as Lord President, a position he was first to hold. Refusing the possibility of his civilisation being destroyed by the Daleks, Rassilon prepared a doomsday scenario, the so-called "Ultimate Sanction". This genocidal scheme included sacrificing all of time itself, thereby destroying the Daleks and all life in the universe. The Time Lords themselves would have transcended into a non-corporeal collective consciousness that would be the only sentient form of life in existence. The Time Lords, apparently hardened by the horrors of war, gave near-unanimous support for this plan – only two Time Lords dissented when the issue was put to a full vote. Prior to the vote, when one of the Council, the Partisan, suggested shelving the Ultimate Sanction and that it may be better if Gallifrey were destroyed, Rassilon disintegrated her.While the High Council continued to lead Time Lord society during the war, a separate War Council was tasked with overseeing the war itself, as well as Gallifrey's defences. The War Council was led by an unknown Time Lord general. During the last days of the Time War, the War Council apparently became disillusioned with the High Council.
|
participant
| 118 |
[
"contributor",
"member",
"participant",
"player",
"agent"
] | null | null |
[
"HE 1523-0901",
"instance of",
"Population II star"
] |
HE 1523-0901, also named TYC 5594-576-1 or 2MASS J15260106-0911388, is the designation given to a red giant star in the Milky Way galaxy approximately 10,000 light years from Earth. It is thought to be a second generation, Population II, or metal-poor, star ([Fe/H] = −2.95). The star was found in the sample of bright metal-poor halo stars from the Hamburg/ESO Survey by Anna Frebel and collaborators. The group's research was published in the May 10, 2007 issue of The Astrophysical Journal.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"HE 1523-0901",
"instance of",
"red giant"
] |
HE 1523-0901, also named TYC 5594-576-1 or 2MASS J15260106-0911388, is the designation given to a red giant star in the Milky Way galaxy approximately 10,000 light years from Earth. It is thought to be a second generation, Population II, or metal-poor, star ([Fe/H] = −2.95). The star was found in the sample of bright metal-poor halo stars from the Hamburg/ESO Survey by Anna Frebel and collaborators. The group's research was published in the May 10, 2007 issue of The Astrophysical Journal.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"HE 1523-0901",
"discoverer or inventor",
"Anna Frebel"
] |
HE 1523-0901, also named TYC 5594-576-1 or 2MASS J15260106-0911388, is the designation given to a red giant star in the Milky Way galaxy approximately 10,000 light years from Earth. It is thought to be a second generation, Population II, or metal-poor, star ([Fe/H] = −2.95). The star was found in the sample of bright metal-poor halo stars from the Hamburg/ESO Survey by Anna Frebel and collaborators. The group's research was published in the May 10, 2007 issue of The Astrophysical Journal.
|
discoverer or inventor
| 110 |
[
"discoverer",
"inventor",
"creator",
"pioneer",
"innovator"
] | null | null |
[
"Cayrel's Star",
"instance of",
"Population II star"
] |
BPS CS31082-0001, named Cayrel's Star , is an old Population II star located in a distance of 2.1 kpc in the galactic halo. It belongs to the class of ultra-metal-poor stars (metallicity [Fe/H] = -2.9), specifically the very rare subclass of neutron-capture enhanced stars. It was discovered by Tim C. Beers and collaborators with the Curtis Schmidt telescope at the Cerro Tololo Inter-American Observatory in Chile and analyzed by Roger Cayrel and collaborators. They used the Very Large Telescope (VLT) at the European Southern Observatory in Paranal, Chile for high-resolution optical spectroscopy to determine elemental abundances. The thorium-232 to uranium-238 ratio was used to determine the age. It is estimated to be about 12.5 billion years old, making it one of the oldest known.
Compared to other ultra-metal-poor, r-process enriched stars (as CS22892-052, BD +17° 3248, HE 1523-0901) CS31082-001 has higher abundances of the actinides (Th, U), but a surprisingly low Pb abundance.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"Cayrel's Star",
"named after",
"Roger Cayrel"
] |
BPS CS31082-0001, named Cayrel's Star , is an old Population II star located in a distance of 2.1 kpc in the galactic halo. It belongs to the class of ultra-metal-poor stars (metallicity [Fe/H] = -2.9), specifically the very rare subclass of neutron-capture enhanced stars. It was discovered by Tim C. Beers and collaborators with the Curtis Schmidt telescope at the Cerro Tololo Inter-American Observatory in Chile and analyzed by Roger Cayrel and collaborators. They used the Very Large Telescope (VLT) at the European Southern Observatory in Paranal, Chile for high-resolution optical spectroscopy to determine elemental abundances. The thorium-232 to uranium-238 ratio was used to determine the age. It is estimated to be about 12.5 billion years old, making it one of the oldest known.
Compared to other ultra-metal-poor, r-process enriched stars (as CS22892-052, BD +17° 3248, HE 1523-0901) CS31082-001 has higher abundances of the actinides (Th, U), but a surprisingly low Pb abundance.
|
named after
| 11 |
[
"called after",
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"called for"
] | null | null |
[
"Precambrian",
"part of",
"geologic time scale"
] |
Overview
Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from the Precambrian (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.It is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma.The term "Precambrian" is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey and the International Commission on Stratigraphy regard the term as informal. Because the span of time falling under the Precambrian consists of three eons (the Hadean, the Archean, and the Proterozoic), it is sometimes described as a supereon, but this is also an informal term, not defined by the ICS in its chronostratigraphic guide.Eozoic (from eo- "earliest") was a synonym for pre-Cambrian, or more specifically Archean.
|
part of
| 15 |
[
"a component of",
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"a fragment of",
"a portion of"
] | null | null |
[
"Precambrian",
"followed by",
"Phanerozoic"
] |
Overview
Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from the Precambrian (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.It is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma.The term "Precambrian" is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey and the International Commission on Stratigraphy regard the term as informal. Because the span of time falling under the Precambrian consists of three eons (the Hadean, the Archean, and the Proterozoic), it is sometimes described as a supereon, but this is also an informal term, not defined by the ICS in its chronostratigraphic guide.Eozoic (from eo- "earliest") was a synonym for pre-Cambrian, or more specifically Archean.
|
followed by
| 17 |
[
"succeeded by",
"later followed by",
"came after"
] | null | null |
[
"Precambrian",
"has part(s)",
"Proterozoic"
] |
Subdivisions
A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed absolute dates to be assigned to specific formations and features. The Precambrian is divided into three eons: the Hadean (4567.3–4000 Ma), Archean (4000-2500 Ma) and Proterozoic (2500-538.8 Ma). See Timetable of the Precambrian.Proterozoic: this eon refers to the time from the lower Cambrian boundary, 538.8 Ma, back through 2500 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary. The Proterozoic Eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.
Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary (538.8 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American stratigraphy.
Ediacaran: The youngest geologic period within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from 538.8 to 635 Ma. In this period the Ediacaran biota appeared.
Cryogenian: The middle period in the Neoproterozoic Era: 635-720 Ma.
Tonian: the earliest period of the Neoproterozoic Era: 720-1000 Ma.
Mesoproterozoic: the middle era of the Proterozoic Eon, 1000-1600 Ma. Corresponds to "Precambrian Y" rocks of older North American stratigraphy.
Paleoproterozoic: oldest era of the Proterozoic Eon, 1600-2500 Ma. Corresponds to "Precambrian X" rocks of older North American stratigraphy.
Archean Eon: 2500-4000 Ma.
Hadean Eon: 4000–4567.3 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites.It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs. The Precambrian could be divided into five "natural" eons, characterized as follows:
Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event.
Hadean: dominated by heavy bombardment from about 4.51 Ga (possibly including a Cool Early Earth period) to the end of the Late Heavy Bombardment period.
Archean: a period defined by the first crustal formations (the Isua greenstone belt) until the deposition of banded iron formations due to increasing atmospheric oxygen content.
Transition: a period of continued iron banded formation until the first continental red beds.
Proterozoic: a period of modern plate tectonics until the first animals.
|
has part(s)
| 19 |
[
"contains",
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"consists of",
"has components"
] | null | null |
[
"Precambrian",
"has part(s)",
"Archaean"
] |
Subdivisions
A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed absolute dates to be assigned to specific formations and features. The Precambrian is divided into three eons: the Hadean (4567.3–4000 Ma), Archean (4000-2500 Ma) and Proterozoic (2500-538.8 Ma). See Timetable of the Precambrian.Proterozoic: this eon refers to the time from the lower Cambrian boundary, 538.8 Ma, back through 2500 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary. The Proterozoic Eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.
Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary (538.8 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American stratigraphy.
Ediacaran: The youngest geologic period within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from 538.8 to 635 Ma. In this period the Ediacaran biota appeared.
Cryogenian: The middle period in the Neoproterozoic Era: 635-720 Ma.
Tonian: the earliest period of the Neoproterozoic Era: 720-1000 Ma.
Mesoproterozoic: the middle era of the Proterozoic Eon, 1000-1600 Ma. Corresponds to "Precambrian Y" rocks of older North American stratigraphy.
Paleoproterozoic: oldest era of the Proterozoic Eon, 1600-2500 Ma. Corresponds to "Precambrian X" rocks of older North American stratigraphy.
Archean Eon: 2500-4000 Ma.
Hadean Eon: 4000–4567.3 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites.It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs. The Precambrian could be divided into five "natural" eons, characterized as follows:
Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event.
Hadean: dominated by heavy bombardment from about 4.51 Ga (possibly including a Cool Early Earth period) to the end of the Late Heavy Bombardment period.
Archean: a period defined by the first crustal formations (the Isua greenstone belt) until the deposition of banded iron formations due to increasing atmospheric oxygen content.
Transition: a period of continued iron banded formation until the first continental red beds.
Proterozoic: a period of modern plate tectonics until the first animals.
|
has part(s)
| 19 |
[
"contains",
"comprises",
"includes",
"consists of",
"has components"
] | null | null |
[
"Precambrian",
"has part(s)",
"Hadean"
] |
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.
The Precambrian is an informal unit of geologic time, subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago (Ga) to the beginning of the Cambrian Period, about 538.8 million years ago (Ma), when hard-shelled creatures first appeared in abundance.Overview
Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from the Precambrian (e.g. stromatolites) are of limited biostratigraphic use. This is because many Precambrian rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.It is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma.The term "Precambrian" is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey and the International Commission on Stratigraphy regard the term as informal. Because the span of time falling under the Precambrian consists of three eons (the Hadean, the Archean, and the Proterozoic), it is sometimes described as a supereon, but this is also an informal term, not defined by the ICS in its chronostratigraphic guide.Eozoic (from eo- "earliest") was a synonym for pre-Cambrian, or more specifically Archean.Subdivisions
A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed absolute dates to be assigned to specific formations and features. The Precambrian is divided into three eons: the Hadean (4567.3–4000 Ma), Archean (4000-2500 Ma) and Proterozoic (2500-538.8 Ma). See Timetable of the Precambrian.Proterozoic: this eon refers to the time from the lower Cambrian boundary, 538.8 Ma, back through 2500 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary. The Proterozoic Eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.
Neoproterozoic: The youngest geologic era of the Proterozoic Eon, from the Cambrian Period lower boundary (538.8 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American stratigraphy.
Ediacaran: The youngest geologic period within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from 538.8 to 635 Ma. In this period the Ediacaran biota appeared.
Cryogenian: The middle period in the Neoproterozoic Era: 635-720 Ma.
Tonian: the earliest period of the Neoproterozoic Era: 720-1000 Ma.
Mesoproterozoic: the middle era of the Proterozoic Eon, 1000-1600 Ma. Corresponds to "Precambrian Y" rocks of older North American stratigraphy.
Paleoproterozoic: oldest era of the Proterozoic Eon, 1600-2500 Ma. Corresponds to "Precambrian X" rocks of older North American stratigraphy.
Archean Eon: 2500-4000 Ma.
Hadean Eon: 4000–4567.3 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites.It has been proposed that the Precambrian should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs. The Precambrian could be divided into five "natural" eons, characterized as follows:
Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event.
Hadean: dominated by heavy bombardment from about 4.51 Ga (possibly including a Cool Early Earth period) to the end of the Late Heavy Bombardment period.
Archean: a period defined by the first crustal formations (the Isua greenstone belt) until the deposition of banded iron formations due to increasing atmospheric oxygen content.
Transition: a period of continued iron banded formation until the first continental red beds.
Proterozoic: a period of modern plate tectonics until the first animals.
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Etymology
"Hadean" (from Hades, the Greek god of the underworld, and the underworld itself) describes the hellish conditions then prevailing on Earth: the planet had just formed and was still very hot owing to its recent accretion, the abundance of short-lived radioactive elements, and frequent collisions with other Solar System bodies.
The term was coined by American geologist Preston Cloud, after the Greek mythical underworld Hades, originally to label the period before the earliest-known rocks on Earth. W. Brian Harland later coined an almost synonymous term, the Priscoan Period, from priscus, the Latin word for 'ancient'. Other, older texts refer to the eon as the Pre-Archean.
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The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.Description
Pre-Nectarian rocks are rare in the lunar sample suite; they are mostly composed of lunar highlands material which have been heavily churned, brecciated, and thermally affected by subsequent impacts, particularly during the Heavy Bombardment Eon (HBE; a period of 0.6-1 Gy from the formation of the Moon until at least the formation of the Imbrium Basin ~3.9 Ga, or even later with the formation of Orientalis Basin) that marks the approximate beginning of the Nectarian period. The primary pre-Nectarian lunar highland material is dominated by the rock type anorthosite, which suggests that the early stage of lunar crustal formation occurred via mineral crystallization of a global magma ocean.
This geologic period has been informally subdivided into the Cryptic Era (4.533 - 4.172 Ga ago) and Basin Groups 1-9 (4.172 - 3.92 Ga ago), but these divisions are not used on any geologic maps. Similarly the later period has also been called the Aitkenian period.
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The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.
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significant event
| 30 |
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The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.
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The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.
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[
"Theia (planet)",
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Name
Theia was named after Theia, one of the Titans, who in Greek mythology was the mother of Selene, the goddess of the Moon, which parallels the planet Theia's collision with the early Earth that is theorized to have created the Moon. In modern Greek, it has the same origin as the words "θείος" (theios) and "θεία" (theia) ('uncle' and 'aunt', also meaning 'divine' in Ancient Greek).
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[
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Theia is a hypothesized ancient planet in the early Solar System that, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, with some of the resulting ejected debris gathering to form the Moon.
Theia could explain why Earth's core is larger than expected for a body its size, with Theia's core and mantle fusing with those of Earth.
Theia is hypothesized to have been about the size of Mars. Theia may have formed in the outer Solar System and provided much of Earth's water.
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"Noachian",
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Description and name origin
The Noachian System and Period is named after Noachis Terra (lit. "Land of Noah"), a heavily cratered highland region west of the Hellas basin. The type area of the Noachian System is in the Noachis quadrangle (MC-27) around 40°S 340°W. At a large scale (>100 m), Noachian surfaces are very hilly and rugged, superficially resembling the lunar highlands. Noachian terrains consist of overlapping and interbedded ejecta blankets of many old craters. Mountainous rim materials and uplifted basement rock from large impact basins are also common. (See Anseris Mons, for example.) The number-density of large impact craters is very high, with about 200 craters greater than 16 km in diameter per million km2. Noachian-aged units cover 45% of the Martian surface; they occur mainly in the southern highlands of the planet, but are also present over large areas in the north, such as in Tempe and Xanthe Terrae, Acheron Fossae, and around the Isidis basin (Libya Montes).
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The Genesis Rock (sample 15415) is a sample of Moon rock retrieved by Apollo 15 astronauts James Irwin and David Scott in 1971 during the second lunar EVA, at Spur crater. With a mass of c. 270 grams (4,200 grains), it is currently stored at the Lunar Sample Laboratory Facility in Houston, Texas.Rock
Chemical analysis of the Genesis Rock indicated it is an anorthosite, composed mostly of a type of plagioclase feldspar known as anorthite. The rock was formed in the early stages of the Solar System, at least 4 billion years ago.It was originally thought they had found a piece of the Moon's primordial crust, but later analysis initially showed that the rock was only 4.1 ± 0.1 billion years old, which is younger than the Moon itself, and was formed after the Moon's crust solidified. It is still an extremely old sample, formed during the Pre-Nectarian period of the Moon's history. Dating of pyroxenes from other lunar anorthosite samples gave a samarium–neodymium age of crystallization of 4.46 billion years.
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location
| 29 |
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Rock
Chemical analysis of the Genesis Rock indicated it is an anorthosite, composed mostly of a type of plagioclase feldspar known as anorthite. The rock was formed in the early stages of the Solar System, at least 4 billion years ago.It was originally thought they had found a piece of the Moon's primordial crust, but later analysis initially showed that the rock was only 4.1 ± 0.1 billion years old, which is younger than the Moon itself, and was formed after the Moon's crust solidified. It is still an extremely old sample, formed during the Pre-Nectarian period of the Moon's history. Dating of pyroxenes from other lunar anorthosite samples gave a samarium–neodymium age of crystallization of 4.46 billion years.
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has part(s)
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"Genesis Rock",
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The Genesis Rock (sample 15415) is a sample of Moon rock retrieved by Apollo 15 astronauts James Irwin and David Scott in 1971 during the second lunar EVA, at Spur crater. With a mass of c. 270 grams (4,200 grains), it is currently stored at the Lunar Sample Laboratory Facility in Houston, Texas.
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"Genesis Rock",
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Rock
Chemical analysis of the Genesis Rock indicated it is an anorthosite, composed mostly of a type of plagioclase feldspar known as anorthite. The rock was formed in the early stages of the Solar System, at least 4 billion years ago.It was originally thought they had found a piece of the Moon's primordial crust, but later analysis initially showed that the rock was only 4.1 ± 0.1 billion years old, which is younger than the Moon itself, and was formed after the Moon's crust solidified. It is still an extremely old sample, formed during the Pre-Nectarian period of the Moon's history. Dating of pyroxenes from other lunar anorthosite samples gave a samarium–neodymium age of crystallization of 4.46 billion years.
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time period
| 97 |
[
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"Genesis Rock",
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The Genesis Rock (sample 15415) is a sample of Moon rock retrieved by Apollo 15 astronauts James Irwin and David Scott in 1971 during the second lunar EVA, at Spur crater. With a mass of c. 270 grams (4,200 grains), it is currently stored at the Lunar Sample Laboratory Facility in Houston, Texas.
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collection
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The Archean Eon (IPA: ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4,000 to 2,500 million years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's ocean. Except for some trace minerals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The earliest known life started in the Archean. Life was simple throughout the Archean, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free oxygen.
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The Archean Eon (IPA: ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4,000 to 2,500 million years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's ocean. Except for some trace minerals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The earliest known life started in the Archean. Life was simple throughout the Archean, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free oxygen.
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The Archean Eon (IPA: ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4,000 to 2,500 million years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's ocean. Except for some trace minerals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The earliest known life started in the Archean. Life was simple throughout the Archean, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free oxygen.Early life
The processes that gave rise to life on Earth are not completely understood, but there is substantial evidence that life came into existence either near the end of the Hadean Eon or early in the Archean Eon.
The earliest evidence for life on Earth is graphite of biogenic origin found in 3.7 billion–year-old metasedimentary rocks discovered in Western Greenland.
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The Archean Eon (IPA: ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4,000 to 2,500 million years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's ocean. Except for some trace minerals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The earliest known life started in the Archean. Life was simple throughout the Archean, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free oxygen.
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has part(s)
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"Archean",
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The Archean Eon (IPA: ar-KEE-ən, also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4,000 to 2,500 million years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth during the Archean was mostly a water world: there was continental crust, but much of it was under an ocean deeper than today's ocean. Except for some trace minerals, today's oldest continental crust dates back to the Archean. Much of the geological detail of the Archean has been destroyed by subsequent activity. The earliest known life started in the Archean. Life was simple throughout the Archean, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free oxygen.
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Early life
The processes that gave rise to life on Earth are not completely understood, but there is substantial evidence that life came into existence either near the end of the Hadean Eon or early in the Archean Eon.
The earliest evidence for life on Earth is graphite of biogenic origin found in 3.7 billion–year-old metasedimentary rocks discovered in Western Greenland.The earliest identifiable fossils consist of stromatolites, which are microbial mats formed in shallow water by cyanobacteria. The earliest stromatolites are found in 3.48 billion-year-old sandstone discovered in Western Australia. Stromatolites are found throughout the Archean and become common late in the Archean.: 307 Cyanobacteria were instrumental in creating free oxygen in the atmosphere.Further evidence for early life is found in 3.47 billion-year-old baryte, in the Warrawoona Group of Western Australia. This mineral shows sulfur fractionation of as much as 21.1%, which is evidence of sulfate-reducing bacteria that metabolize sulfur-32 more readily than sulfur-34.Evidence of life in the Late Hadean is more controversial. In 2015, biogenic carbon was detected in zircons dated to 4.1 billion years ago, but this evidence is preliminary and needs validation.Earth was very hostile to life before 4.2–4.3 Ga and the conclusion is that before the Archean Eon, life as we know it would have been challenged by these environmental conditions. While life could have arisen before the Archean, the conditions necessary to sustain life could not have occurred until the Archean Eon.Life in the Archean was limited to simple single-celled organisms (lacking nuclei), called prokaryotes. In addition to the domain Bacteria, microfossils of the domain Archaea have also been identified. There are no known eukaryotic fossils from the earliest Archean, though they might have evolved during the Archean without leaving any.: 306, 323 Fossil steranes, indicative of eukaryotes, have been reported from Archean strata but were shown to derive from contamination with younger organic matter. No fossil evidence has been discovered for ultramicroscopic intracellular replicators such as viruses.
Fossilized microbes from terrestrial microbial mats show that life was already established on land 3.22 billion years ago.
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Chronology
The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of the Early Archean Eon (which is now an obsolete name) alongside the Paleoarchean Era.The International Commission on Stratigraphy now officially recognizes the Eoarchean Era as the
first part of the Archaean Eon, preceded by the Hadean Eon, during which the Earth is believed to have been essentially molten.
The Eoarchaean's lower boundary or starting point of 4 Gya (4 billion years ago) is officially recognized by the International Commission on Stratigraphy.The name comes from two Greek words: eos (dawn) and archaios (ancient). The first supercontinent candidate Vaalbara appeared around the end of this period at about 3,600 million years ago.
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[
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Chronology
The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of the Early Archean Eon (which is now an obsolete name) alongside the Paleoarchean Era.The International Commission on Stratigraphy now officially recognizes the Eoarchean Era as the
first part of the Archaean Eon, preceded by the Hadean Eon, during which the Earth is believed to have been essentially molten.
The Eoarchaean's lower boundary or starting point of 4 Gya (4 billion years ago) is officially recognized by the International Commission on Stratigraphy.The name comes from two Greek words: eos (dawn) and archaios (ancient). The first supercontinent candidate Vaalbara appeared around the end of this period at about 3,600 million years ago.
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[
"Nectarian",
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The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.
|
named after
| 11 |
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[
"Nectarian",
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"lunar geologic timescale"
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The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.
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[
"Nectarian",
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The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.Relationship to Earth's geologic time scale
Since little or no geological evidence on Earth exists from the time spanned by the Nectarian period of the Moon, the Nectarian has been used by at least one notable scientific work as an unofficial subdivision of the terrestrial Hadean eon.
|
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[
"Nectarian",
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The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris form the upper part of the densely cratered terrain found in lunar highlands.
|
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| 5 |
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[
"Early Imbrian",
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The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.Early Imbrian
In the lunar geologic timescale, the Early Imbrian epoch occurred from 3,850 million years ago to about 3,800 million years ago. It overlaps the end of the Late Heavy Bombardment of the Inner Solar System. The impact that created the huge Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar near side (such as Mare Crisium, Mare Tranquillitatis, Mare Serenitatis, and Mare Fecunditatis) were also formed in this period. These basins filled with basalt mostly during the subsequent Late Imbrian epoch. The Early Imbrian was preceded by the Nectarian.Late Imbrian
In the Lunar geologic timescale, the Late Imbrian epoch occurred between 3800 million years ago to about 3200 million years ago. It was the epoch during which the mantle below the lunar basins partially melted and filled them with basalt. The melting is thought to have occurred because the impacts of the Early Imbrian thinned the overlying rock – either causing the mantle to rise because of the reduced pressure on it, bringing molten material closer to the surface, or the top melting as heat flowed upwards through the mantle because of reduced overlying thermal insulation. The majority of lunar samples returned to earth for study come from this epoch.
The Earth equivalent consists of half of the Archean eon.
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followed by
| 17 |
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[
"Early Imbrian",
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The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.Early Imbrian
In the lunar geologic timescale, the Early Imbrian epoch occurred from 3,850 million years ago to about 3,800 million years ago. It overlaps the end of the Late Heavy Bombardment of the Inner Solar System. The impact that created the huge Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar near side (such as Mare Crisium, Mare Tranquillitatis, Mare Serenitatis, and Mare Fecunditatis) were also formed in this period. These basins filled with basalt mostly during the subsequent Late Imbrian epoch. The Early Imbrian was preceded by the Nectarian.
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"epoch"
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The Imbrian is a lunar geologic period divided into two epochs, the Early and Late.Early Imbrian
In the lunar geologic timescale, the Early Imbrian epoch occurred from 3,850 million years ago to about 3,800 million years ago. It overlaps the end of the Late Heavy Bombardment of the Inner Solar System. The impact that created the huge Mare Imbrium basin occurred at the start of the epoch. The other large basins that dominate the lunar near side (such as Mare Crisium, Mare Tranquillitatis, Mare Serenitatis, and Mare Fecunditatis) were also formed in this period. These basins filled with basalt mostly during the subsequent Late Imbrian epoch. The Early Imbrian was preceded by the Nectarian.Late Imbrian
In the Lunar geologic timescale, the Late Imbrian epoch occurred between 3800 million years ago to about 3200 million years ago. It was the epoch during which the mantle below the lunar basins partially melted and filled them with basalt. The melting is thought to have occurred because the impacts of the Early Imbrian thinned the overlying rock – either causing the mantle to rise because of the reduced pressure on it, bringing molten material closer to the surface, or the top melting as heat flowed upwards through the mantle because of reduced overlying thermal insulation. The majority of lunar samples returned to earth for study come from this epoch.
The Earth equivalent consists of half of the Archean eon.
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[
"Archaea",
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"taxon"
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Archaea ( (listen) ar-KEE-ə; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), but this term has fallen out of use.Archaeal cells have unique properties separating them from the other two domains, Bacteria and Eukaryota. Archaea are further divided into multiple recognized phyla. Classification is difficult because most have not been isolated in a laboratory and have been detected only by their gene sequences in environmental samples. It is unknown if these are able to produce endospores.
Archaea and bacteria are generally similar in size and shape, although a few archaea have very different shapes, such as the flat, square cells of Haloquadratum walsbyi. Despite this morphological similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably for the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. Archaea use more diverse energy sources than eukaryotes, ranging from organic compounds such as sugars, to ammonia, metal ions or even hydrogen gas. The salt-tolerant Haloarchaea use sunlight as an energy source, and other species of archaea fix carbon (autotrophy), but unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria, no known species of Archaea form endospores.
The first observed archaea were extremophiles, living in extreme environments such as hot springs and salt lakes with no other organisms. Improved molecular detection tools led to the discovery of archaea in almost every habitat, including soil, oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet.
Archaea are a major part of Earth's life. They are part of the microbiota of all organisms. In the human microbiome, they are important in the gut, mouth, and on the skin. Their morphological, metabolic, and geographical diversity permits them to play multiple ecological roles: carbon fixation; nitrogen cycling; organic compound turnover; and maintaining microbial symbiotic and syntrophic communities, for example.No clear examples of archaeal pathogens or parasites are known. Instead they are often mutualists or commensals, such as the methanogens (methane-producing strains) that inhabit the gastrointestinal tract in humans and ruminants, where their vast numbers facilitate digestion. Methanogens are also used in biogas production and sewage treatment, and biotechnology exploits enzymes from extremophile archaea that can endure high temperatures and organic solvents.
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[
"Archaea",
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"Carl Woese"
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Discovery and classification
Early concept
For much of the 20th century, prokaryotes were regarded as a single group of organisms and classified based on their biochemistry, morphology and metabolism. Microbiologists tried to classify microorganisms based on the structures of their cell walls, their shapes, and the substances they consume. In 1965, Emile Zuckerkandl and Linus Pauling instead proposed using the sequences of the genes in different prokaryotes to work out how they are related to each other. This phylogenetic approach is the main method used today.Archaea were first classified separately from bacteria in 1977 by Carl Woese and George E. Fox, based on their ribosomal RNA (rRNA) genes. (At that time only the methanogens were known). They called these groups the Urkingdoms of Archaebacteria and Eubacteria, though other researchers treated them as kingdoms or subkingdoms. Woese and Fox gave the first evidence for Archaebacteria as a separate "line of descent": 1. lack of peptidoglycan in their cell walls, 2. two unusual coenzymes, 3. results of 16S ribosomal RNA gene sequencing. To emphasize this difference, Woese, Otto Kandler and Mark Wheelis later proposed reclassifying organisms into three natural domains known as the three-domain system: the Eukarya, the Bacteria and the Archaea, in what is now known as the Woesian Revolution.The word archaea comes from the Ancient Greek ἀρχαῖα, meaning "ancient things", as the first representatives of the domain Archaea were methanogens and it was assumed that their metabolism reflected Earth's primitive atmosphere and the organisms' antiquity, but as new habitats were studied, more organisms were discovered. Extreme halophilic and hyperthermophilic microbes were also included in Archaea. For a long time, archaea were seen as extremophiles that exist only in extreme habitats such as hot springs and salt lakes, but by the end of the 20th century, archaea had been identified in non-extreme environments as well. Today, they are known to be a large and diverse group of organisms abundantly distributed throughout nature. This new appreciation of the importance and ubiquity of archaea came from using polymerase chain reaction (PCR) to detect prokaryotes from environmental samples (such as water or soil) by multiplying their ribosomal genes. This allows the detection and identification of organisms that have not been cultured in the laboratory.Comparison with other domains
The following table compares some major characteristics of the three domains, to illustrate their similarities and differences.
Archaea were split off as a third domain because of the large differences in their ribosomal RNA structure. The particular molecule 16S rRNA is key to the production of proteins in all organisms. Because this function is so central to life, organisms with mutations in their 16S rRNA are unlikely to survive, leading to great (but not absolute) stability in the structure of this polynucleotide over generations. 16S rRNA is large enough to show organism-specific variations, but still small enough to be compared quickly. In 1977, Carl Woese, a microbiologist studying the genetic sequences of organisms, developed a new comparison method that involved splitting the RNA into fragments that could be sorted and compared with other fragments from other organisms. The more similar the patterns between species, the more closely they are related.Woese used his new rRNA comparison method to categorize and contrast different organisms. He compared a variety of species and happened upon a group of methanogens with rRNA vastly different from any known prokaryotes or eukaryotes. These methanogens were much more similar to each other than to other organisms, leading Woese to propose the new domain of Archaea. His experiments showed that the archaea were genetically more similar to eukaryotes than prokaryotes, even though they were more similar to prokaryotes in structure. This led to the conclusion that Archaea and Eukarya shared a common ancestor more recent than Eukarya and Bacteria. The development of the nucleus occurred after the split between Bacteria and this common ancestor.One property unique to archaea is the abundant use of ether-linked lipids in their cell membranes. Ether linkages are more chemically stable than the ester linkages found in bacteria and eukarya, which may be a contributing factor to the ability of many archaea to survive in extreme environments that place heavy stress on cell membranes, such as extreme heat and salinity. Comparative analysis of archaeal genomes has also identified several molecular conserved signature indels and signature proteins uniquely present in either all archaea or different main groups within archaea. Another unique feature of archaea, found in no other organisms, is methanogenesis (the metabolic production of methane). Methanogenic archaea play a pivotal role in ecosystems with organisms that derive energy from oxidation of methane, many of which are bacteria, as they are often a major source of methane in such environments and can play a role as primary producers. Methanogens also play a critical role in the carbon cycle, breaking down organic carbon into methane, which is also a major greenhouse gas.This difference in the biochemical structure of Bacteria and Archaea has been explained by researchers through evolutionary processes. It is theorized that both domains originated at deep sea alkaline hydrothermal vents. At least twice, microbes evolved lipid biosynthesis and cell wall biochemistry. These parallel origins founded the separate lineages Archaea and Bacteria. It has been suggested that the last universal common ancestor was a not free-living organism. However this view has been challenged by other researchers and is currently in dispute.
|
discoverer or inventor
| 110 |
[
"discoverer",
"inventor",
"creator",
"pioneer",
"innovator"
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[
"Prokaryote",
"has part(s)",
"prokaryotic cell"
] |
A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word prokaryote comes from the Greek πρό (pro, 'before') and κάρυον (karyon, 'nut' or 'kernel'). In the two-empire system arising from the work of Édouard Chatton, prokaryotes were classified within the empire Prokaryota. But in the three-domain system, based upon molecular analysis, prokaryotes are divided into two domains: Bacteria (formerly Eubacteria) and Archaea (formerly Archaebacteria). Organisms with nuclei are placed in a third domain, Eukaryota. In biological evolution, prokaryotes are deemed to have arisen before eukaryotes.
Besides the absence of a nucleus, prokaryotes also lack mitochondria, or most of the other membrane-bound organelles that characterize the eukaryotic cell. It was once thought that prokaryotic cellular components within the cytoplasm were unenclosed, except for an outer cell membrane, but bacterial microcompartments, which are thought to be simple organelles enclosed in protein shells, have been discovered, along with other prokaryotic organelles. While being unicellular, some prokaryotes, such as cyanobacteria, may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles. Prokaryotes are asexual, reproducing without fusion of gametes, although horizontal gene transfer may take place.
Molecular studies have provided insight into the evolution and interrelationships of the three domains of life. The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization; only eukaryotic cells have an enveloped nucleus that contains its chromosomal DNA, and other characteristic membrane-bound organelles including mitochondria. Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments.
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has part(s)
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[
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[
"Eratosthenian",
"part of",
"lunar geologic timescale"
] |
The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface that is not significantly eroded by subsequent impacts, but which also does not possess a ray system. The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time. The youngest lunar lava flows identified from orbital images are tentatively placed near the end of this period.
Its Earth equivalent consists of most of the Mesoarchean and Neoarchean eras (Archean eon), Paleoproterozoic and Mesoproterozoic eras (Proterozoic eon).
|
part of
| 15 |
[
"a component of",
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"a fragment of",
"a portion of"
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[
"Eratosthenian",
"named after",
"Eratosthenes"
] |
The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface that is not significantly eroded by subsequent impacts, but which also does not possess a ray system. The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time. The youngest lunar lava flows identified from orbital images are tentatively placed near the end of this period.
Its Earth equivalent consists of most of the Mesoarchean and Neoarchean eras (Archean eon), Paleoproterozoic and Mesoproterozoic eras (Proterozoic eon).
|
named after
| 11 |
[
"called after",
"named for",
"honored after",
"called for"
] | null | null |
[
"Eratosthenian",
"instance of",
"geological era"
] |
The Eratosthenian period in the lunar geologic timescale runs from 3,200 million years ago to 1,100 million years ago. It is named after the crater Eratosthenes, which displays characteristics typical of craters of this age, including a surface that is not significantly eroded by subsequent impacts, but which also does not possess a ray system. The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time. The youngest lunar lava flows identified from orbital images are tentatively placed near the end of this period.
Its Earth equivalent consists of most of the Mesoarchean and Neoarchean eras (Archean eon), Paleoproterozoic and Mesoproterozoic eras (Proterozoic eon).
|
instance of
| 5 |
[
"type of",
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[
"Opisthokont",
"instance of",
"clade"
] |
The opisthokonts (from Ancient Greek ὀπίσθιος (opísthios) 'rear, posterior', and κοντός (kontós) 'pole, i.e. flagellum') are a broad group of eukaryotes, including both the animal and fungus kingdoms. The opisthokonts, previously called the "Fungi/Metazoa group", are generally recognized as a clade. Opisthokonts together with Apusomonadida and Breviata comprise the larger clade Obazoa.Flagella and other characteristics
A common characteristic of opisthokonts is that flagellate cells, such as the sperm of most animals and the spores of the chytrid fungi, propel themselves with a single posterior flagellum. It is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more anterior flagella. However, in some opisthokont groups, including most of the fungi, flagellate cells have been lost.Opisthokont characteristics include synthesis of extracellular chitin in exoskeleton, cyst/spore wall, or cell wall of filamentous growth and hyphae; the extracellular digestion of substrates with osmotrophic absorption of nutrients; and other cell biosynthetic and metabolic pathways. Genera at the base of each clade are amoeboid and phagotrophic.
|
instance of
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[
"Paleoproterozoic",
"part of",
"Proterozoic"
] |
The Paleoproterozoic Era (IPA: ;, also spelled Palaeoproterozoic), spanning the time period from 2,500 to 1,600 million years ago (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history. It was during this era that the continents first stabilized.Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year.
|
part of
| 15 |
[
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"an element of",
"a fragment of",
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[
"Paleoproterozoic",
"instance of",
"era"
] |
The Paleoproterozoic Era (IPA: ;, also spelled Palaeoproterozoic), spanning the time period from 2,500 to 1,600 million years ago (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's geological history. It was during this era that the continents first stabilized.Paleontological evidence suggests that the Earth's rotational rate ~1.8 billion years ago equated to 20-hour days, implying a total of ~450 days per year.
|
instance of
| 5 |
[
"type of",
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[
"Paleoproterozoic",
"has part(s)",
"Statherian"
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Emergence of Eukarya
Many crown node eukaryotes (from which the modern-day eukaryotic lineages would have arisen) have been approximately dated to around the time of the Paleoproterozoic Era.
While there is some debate as to the exact time at which eukaryotes evolved,
current understanding places it somewhere in this era. Statherian fossils from the Changcheng Group of North China provide evidence that eukaryotic life was already diverse during the late Palaeoproterozoic.
|
has part(s)
| 19 |
[
"contains",
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[
"Siderian",
"named after",
"iron"
] |
The Siderian Period ( ; Ancient Greek: σίδηρος, romanized: sídēros, meaning "iron") is the first geologic period in the Paleoproterozoic Era and lasted from 2500 Ma to 2300 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The deposition of banded iron formations peaked early in this period. These iron rich formations were formed as anaerobic cyanobacteria produced waste oxygen that combined with iron, forming magnetite (Fe3O4, an iron oxide). This process removed iron from the Earth's oceans, presumably turning greenish seas clear. Eventually, with no remaining iron in the oceans to serve as an oxygen sink, the process allowed the buildup of an oxygen-rich atmosphere. This second, follow-on event is known as the oxygen catastrophe, which, some geologists believe triggered the Huronian glaciation.Since the time period from 2420 Ma to 2250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 in a geological timescale review.
|
named after
| 11 |
[
"called after",
"named for",
"honored after",
"called for"
] | null | null |
[
"Siderian",
"part of",
"Paleoproterozoic"
] |
The Siderian Period ( ; Ancient Greek: σίδηρος, romanized: sídēros, meaning "iron") is the first geologic period in the Paleoproterozoic Era and lasted from 2500 Ma to 2300 Ma (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The deposition of banded iron formations peaked early in this period. These iron rich formations were formed as anaerobic cyanobacteria produced waste oxygen that combined with iron, forming magnetite (Fe3O4, an iron oxide). This process removed iron from the Earth's oceans, presumably turning greenish seas clear. Eventually, with no remaining iron in the oceans to serve as an oxygen sink, the process allowed the buildup of an oxygen-rich atmosphere. This second, follow-on event is known as the oxygen catastrophe, which, some geologists believe triggered the Huronian glaciation.Since the time period from 2420 Ma to 2250 Ma is well-defined by the lower edge of iron-deposition layers, an alternative period named the Oxygenian, based on stratigraphy instead of chronometry, was suggested in 2012 in a geological timescale review.
|
part of
| 15 |
[
"a component of",
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"a fragment of",
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] | null | null |
[
"Rhyacian",
"part of",
"Paleoproterozoic"
] |
The Rhyacian Period ( ; Ancient Greek: ῥύαξ, romanized: rhýax, meaning "stream of lava") is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The Bushveld Igneous Complex and some other similar intrusions formed during this period.The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period.For the time interval from 2250 Ma to 2060 Ma, an alternative period based on stratigraphy rather than chronometry, named either the Jatulian or the Eukaryian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of March 2020, this has not yet been officially adopted by the IUGS. The term Jatulian is, however, used in the regional stratigraphy of the Paleoproterozoic rocks of Fennoscandia.This is when the eukaryotes are thought to have originated from the symbiosis between asgardarchaea and alphaproteobacteria, as well as the sexual reproduction found within the eukaryotes only, thus the alternative name Eukaryian.
|
part of
| 15 |
[
"a component of",
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"an element of",
"a fragment of",
"a portion of"
] | null | null |
[
"Rhyacian",
"instance of",
"period"
] |
The Rhyacian Period ( ; Ancient Greek: ῥύαξ, romanized: rhýax, meaning "stream of lava") is the second geologic period in the Paleoproterozoic Era and lasted from 2300 Mya to 2050 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The Bushveld Igneous Complex and some other similar intrusions formed during this period.The Huronian (Makganyene) global glaciation began at the start of the Rhyacian and lasted 100 million years. It lasted about 80% of this period.For the time interval from 2250 Ma to 2060 Ma, an alternative period based on stratigraphy rather than chronometry, named either the Jatulian or the Eukaryian, was suggested in the geological timescale review 2012 edited by Gradstein et al., but as of March 2020, this has not yet been officially adopted by the IUGS. The term Jatulian is, however, used in the regional stratigraphy of the Paleoproterozoic rocks of Fennoscandia.This is when the eukaryotes are thought to have originated from the symbiosis between asgardarchaea and alphaproteobacteria, as well as the sexual reproduction found within the eukaryotes only, thus the alternative name Eukaryian.
|
instance of
| 5 |
[
"type of",
"example of",
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"representation of"
] | null | null |
[
"Orosirian",
"named after",
"mountain range"
] |
The Orosirian Period ( ; Ancient Greek: ὀροσειρά, romanized: oroseirá, meaning "mountain range") is the third geologic period in the Paleoproterozoic Era and lasted from 2050 Mya to 1800 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
|
named after
| 11 |
[
"called after",
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"called for"
] | null | null |
[
"Statherian",
"part of",
"Paleoproterozoic"
] |
The Statherian Period ( ; Ancient Greek: σταθερός, romanized: statherós, meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from 1800 Mya to 1600 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The period was characterized on most continents by either new platforms or final cratonization of fold belts. Oxygen levels were 10% to 20% of current values.Rafatazmia, controversially claimed to be present in Statherian beds in India, may be the oldest known confirmably eukaryotic fossil organism.By the beginning of the Statherian, the supercontinent Columbia had assembled.At roughly 1.7 billion years before present a series of natural nuclear fission reactors was operational in what is now Oklo, Gabon.
|
part of
| 15 |
[
"a component of",
"a constituent of",
"an element of",
"a fragment of",
"a portion of"
] | null | null |
[
"Statherian",
"instance of",
"period"
] |
The Statherian Period ( ; Ancient Greek: σταθερός, romanized: statherós, meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from 1800 Mya to 1600 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.The period was characterized on most continents by either new platforms or final cratonization of fold belts. Oxygen levels were 10% to 20% of current values.Rafatazmia, controversially claimed to be present in Statherian beds in India, may be the oldest known confirmably eukaryotic fossil organism.By the beginning of the Statherian, the supercontinent Columbia had assembled.At roughly 1.7 billion years before present a series of natural nuclear fission reactors was operational in what is now Oklo, Gabon.
|
instance of
| 5 |
[
"type of",
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[
"Mesoproterozoic",
"followed by",
"Neoproterozoic"
] |
The Mesoproterozoic Era is a geologic era that occurred from 1,600 to 1,000 million years ago. The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), but little is known about them. The continental masses of the Mesoproterozoic were more or less the same ones that exist today, although their arrangement on the Earth's surface was different.
|
followed by
| 17 |
[
"succeeded by",
"later followed by",
"came after"
] | null | null |
[
"Calymmian",
"part of",
"Mesoproterozoic"
] |
The Calymmian Period (from Ancient Greek: κάλυμμα, romanized: kálymma, meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.
The supercontinent Columbia started to break during the Calymmian some 1500 Mya.
|
part of
| 15 |
[
"a component of",
"a constituent of",
"an element of",
"a fragment of",
"a portion of"
] | null | null |
[
"Calymmian",
"instance of",
"period"
] |
The Calymmian Period (from Ancient Greek: κάλυμμα, romanized: kálymma, meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from 1600 Mya to 1400 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
The period is characterised by expansion of existing platform covers, or by new platforms on recently cratonized basements.
The supercontinent Columbia started to break during the Calymmian some 1500 Mya.
|
instance of
| 5 |
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[
"Archaeplastida",
"instance of",
"clade"
] |
Taxonomy
The consensus in 2005, when the group consisting of the glaucophytes and red and green algae and land plants was named 'Archaeplastida', was that it was a clade, i.e. was monophyletic. Many studies published since then have provided evidence in agreement. Other studies, though, have suggested that the group is paraphyletic. To date, the situation appears unresolved, but a strong signal for Plantae (Archaeplastida) monophyly has been demonstrated in a recent study (with an enrichment of red algal genes). The assumption made here is that Archaeplastida is a valid clade.
Various names have been given to the group. Some authors have simply referred to the group as plants or Plantae. However, the name Plantae is ambiguous, since it has also been applied to less inclusive clades, such as Viridiplantae and embryophytes. To distinguish, the larger group is sometimes known as Plantae sensu lato ("plants in the broad sense").
To avoid ambiguity, other names have been proposed. Primoplantae, which appeared in 2004, seems to be the first new name suggested for this group. Another name applied to this node is Plastida, defined as the clade sharing "plastids of primary (direct prokaryote) origin [as] in Magnolia virginiana Linnaeus 1753".Although many studies have suggested the Archaeplastida form a monophyletic group, a 2009 paper argues that they are in fact paraphyletic. The enrichment of novel red algal genes in a recent study demonstrates a strong signal for Plantae (Archaeplastida) monophyly and an equally strong signal of gene sharing history between the red/green algae and other lineages. This study provides insight on how rich mesophilic red algal gene data are crucial for testing controversial issues in eukaryote evolution and for understanding the complex patterns of gene inheritance in protists.
The name Archaeplastida was proposed in 2005 by a large international group of authors (Adl et al.), who aimed to produce a classification for the eukaryotes which took into account morphology, biochemistry, and phylogenetics, and which had "some stability in the near term." They rejected the use of formal taxonomic ranks in favour of a hierarchical arrangement where the clade names do not signify rank. Thus, the phylum name 'Glaucophyta' and the class name 'Rhodophyceae' appear at the same level in their classification. The divisions proposed for the Archaeplastida are shown below in both tabular and diagrammatic form.Archaeplastida:
|
instance of
| 5 |
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"type of",
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[
"Ectasian",
"part of",
"Mesoproterozoic"
] |
The Ectasian Period (from Ancient Greek: ἔκτασις, romanized: éktasis, meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from 1400 Mya ago to 1200 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Geologically the name refers to the continued expansion of platform covers during this period.
This period is interesting for the first evidence of sexual reproduction. The 1.2 billion years old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells.
Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity. In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.
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The Ectasian Period (from Ancient Greek: ἔκτασις, romanized: éktasis, meaning "extension") is the second geologic period in the Mesoproterozoic Era and lasted from 1400 Mya ago to 1200 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically.
Geologically the name refers to the continued expansion of platform covers during this period.
This period is interesting for the first evidence of sexual reproduction. The 1.2 billion years old Hunting Formation on Somerset Island, Canada, dates from the end of the Ectasian. It contains the microfossils of the multicellular filaments of Bangiomorpha pubescens (type of red algae), the first taxonomically resolved eukaryote. This was the first organism that exhibited sexual reproduction, which is an essential feature for complex multicellularity. Complex multicellularity is different from "simple" multicellularity, such as colonies of organisms living together. True multicellular organisms contain cells that are specialized for different functions. This is, in fact, an essential feature of sexual reproduction as well, since the male and female gametes are specialized cells. Organisms that reproduce sexually must solve the problem of generating an entire organism from just the germ cells.
Sexual reproduction and the ability of gametes to develop into an organism are the necessary antecedents to true multicellularity. In fact, we tend to think of sexual reproduction and true multicellularity as occurring at the same time, and true multicellularity is often taken as a marker for sexual reproduction.
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The Stenian Period (, from Ancient Greek: στενός, romanized: stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from 1200 Mya to 1000 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The name derives from narrow polymetamorphic belts formed over this period.
Preceded by the Ectasian Period and followed by the Neoproterozoic Era.
The supercontinent Rodinia assembled during the Stenian. It would last into the Tonian Period.
This period includes the formation of the Keweenawan Rift at about 1100 Mya.Fossils of the oldest known sexually reproducing organism, Bangiomorpha pubescens, first appeared in the Stenian.
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The Stenian Period (, from Ancient Greek: στενός, romanized: stenós, meaning "narrow") is the final geologic period in the Mesoproterozoic Era and lasted from 1200 Mya to 1000 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The name derives from narrow polymetamorphic belts formed over this period.
Preceded by the Ectasian Period and followed by the Neoproterozoic Era.
The supercontinent Rodinia assembled during the Stenian. It would last into the Tonian Period.
This period includes the formation of the Keweenawan Rift at about 1100 Mya.Fossils of the oldest known sexually reproducing organism, Bangiomorpha pubescens, first appeared in the Stenian.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.Terminal period
The nomenclature for the terminal period of the Neoproterozoic Era has been unstable. Russian and Nordic geologists referred to the last period of the Neoproterozoic as the Vendian, while Chinese geologists referred to it as the Sinian, and most Australians and North Americans used the name Ediacaran.
However, in 2004, the International Union of Geological Sciences ratified the Ediacaran Period to be a geological age of the Neoproterozoic, ranging from 635 to 538.8 (at the time to 542) million years ago. The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic Global Boundary Stratotype Section and Points, rather than the absolute Global Standard Stratigraphic Ages.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.Geology
At the onset of the Neoproterozoic the supercontinent Rodinia, which had assembled during the late Mesoproterozoic, straddled the equator. During the Tonian, rifting commenced which broke Rodinia into a number of individual land masses.
Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the Sturtian and Marinoan glaciations of the Cryogenian Period.
These glaciations are believed to have been so severe that there were ice sheets at the equator—a state known as the "Snowball Earth".Subdivisions
Neoproterozoic time is subdivided into the Tonian (1000–720 Ma), Cryogenian (720–635 Ma) and Ediacaran (635–538.8 Ma) periods.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.Paleobiology
The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of multicellular life at the first appearance of hard-shelled arthropods called trilobites and archeocyathid sponges at the beginning of the Cambrian Period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated the Cambrian. A complex fauna was found in South West Africa in the 1920s but was inaccurately dated. Another fauna was found in South Australia in the 1940s, but it was not thoroughly examined until the late 1950s. Other possible early animal fossils were found in Russia, England, Canada, and elsewhere (see Ediacaran biota). Some were determined to be pseudofossils, but others were revealed to be members of rather complex biotas that remain poorly understood. At least 25 regions worldwide have yielded metazoan fossils older than the classical Precambrian–Cambrian boundary (which is currently dated at 538.8 million years ago).A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like organisms; discoids that might be holdfasts for stalked organisms ("medusoids"); mattress-like forms; small calcareous tubes; and armored animals of unknown provenance.
These were most commonly known as Vendian biota until the formal naming of the Period, and are currently known as Ediacaran Period biota. Most were soft bodied. The relationships, if any, to modern forms are obscure. Some paleontologists relate many or most of these forms to modern animals. Others acknowledge a few possible or even likely relationships but feel that most of the Ediacaran forms are representatives of unknown animal types.
In addition to Ediacaran biota, two other types of biota were discovered in China. The Doushantuo Formation preserves fossils of microscopic marine organisms in great detail. The Hainan biota consists of small worm-shaped organisms.Molecular phylogeny suggests that animals may have emerged even earlier in the Proterozoic, but physical evidence for such animal life is lacking. Possible keratose sponge fossils have been reported in reefs dating back to 890 million years before the present, but remain unconfirmed.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.Subdivisions
Neoproterozoic time is subdivided into the Tonian (1000–720 Ma), Cryogenian (720–635 Ma) and Ediacaran (635–538.8 Ma) periods.
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The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.
The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth".
The earliest fossils of complex multicellular life are found in the Ediacaran Period. These organisms make up the Ediacaran biota, including the oldest definitive animals in the fossil record.
According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.
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The Tonian (from Ancient Greek: τόνος, romanized: tónos, meaning "stretch") is the first geologic period of the Neoproterozoic Era. It lasted from 1000 to 720 Mya (million years ago). Instead of being based on stratigraphy, these dates are defined by the ICS based on radiometric chronometry. The Tonian is preceded by the Stenian Period of the Mesoproterozoic Era and followed by the Cryogenian.
Rifting leading to the breakup of supercontinent Rodinia, which had formed in the mid-Stenian, occurred during this period, starting from 900 to 850 Mya.
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The Tethys Ocean (Greek: Τηθύς Tēthús), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents of Gondwana and Laurasia, before the opening of the Indian and Atlantic oceans during the Cretaceous Period.
It was preceded by the Paleo-Tethys Ocean, which lasted between the Cambrian and the Early Triassic, while the Neotethys formed during the Late Triassic and lasted until the early Eocene (about 50 million years ago) when it completely closed. A portion known as the Paratethys formed during the Late Jurassic, was isolated during the Oligocene (34 million years ago) and lasted up to the Pliocene (about 5 million years ago), when it largely dried out. The ocean basins of Europe and Western Asia, namely the Mediterranean Sea, Black Sea and Caspian Sea, are each remnants of the Paratethys Ocean.See also
Hațeg Island – Prehistoric island
List of ancient oceans – List of Earth's former oceans
Paleo-Tethys Ocean – Ocean on the margin of Gondwana between the Middle Cambrian and Late Triassic
Pannonian Sea – Shallow ancient sea where the Pannonian Basin in Central Europe is today
Paratethys – Prehistoric shallow inland sea in Eurasia
Piemont-Liguria Ocean – Former piece of oceanic crust that is seen as part of the Tethys Ocean
Ruhpolding Formation
Tethyan Trench – Ancient oceanic trench
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Phylogeny and taxonomy within Amoebozoa
From older studies by Cavalier-Smith, Chao & Lewis 2016 and Silar 2016. Also recent phylogeny indicates the Lobosa are paraphyletic: Conosa is sister of the Cutosea.
Phylum Amoebozoa Lühe 1913 emend. Cavalier-Smith 1998 [Amoebobiota; Eumycetozoa Zopf 1884 emend Olive 1975]Clade Discosea Cavalier-Smith 2004 stat. nov. Adl et al. 2018
Order ?Stereomyxida Grell 1971
Order ?Stygamoebida Smirnov & Cavalier-Smith 2011
Class Centramoebia Cavalier-Smith et al. 2016
Order Centramoebida Rogerson & Patterson 2002 em. Cavalier-Smith 2004
Order Himatismenida Page 1987 [Cochliopodiida]
Order Pellitida Page 1987 [Cochliopodiida]
Class Flabellinia Smirnov & Cavalier-Smith 2011 em. Kudryavtsev et al. 2014
Order Thecamoebida Schaeffer 1926 em. Smirnov & Cavalier-Smith 2011
Order Dermamoebida Cavalier-Smith 2004 em. Smirnov & Cavalier-Smith 2011
Order Vannellida Smirnov et al. 2005
Order Dactylopodida Smirnov et al. 2005
Clade Tevosa Kang et al. 2017
Clade Tubulinea Smirnov et al. 2005 stat. nov. Adl et al. 2018
Class Corycidia Kang et al. 2017 stat. nov. Adl et al. 2018
Order Trichosida Moebius 1889
Family Microcoryciidae de Saedeleer 1934
Class Echinamoebia Cavalier-Smith 2016 stat. nov. Adl et al. 2018
Order Echinamoebida Cavalier-Smith 2004 em. 2011
Class Elardia Kang et al. 2017 stat. nov. Adl et al. 2018
Subclass Leptomyxia Cavalier-Smith 2016
Order Leptomyxida Pussard & Pons 1976 em. Page 1987
Subclass Eulobosia Cavalier-Smith 2016
Order Euamoebida Lepşi 1960 em. Cavalier-Smith 2016
Order Arcellinida Kent 1880
Clade Evosea Kang et al. 2017 stat. nov. Adl et al. 2018
Clade Cutosa Cavalier-Smith 2016 stat. nov.
Class Cutosea Cavalier-Smith 2016
Order Squamocutida Cavalier-Smith 2016
Subphylum Conosa Cavalier-Smith 1998 stat. nov.
Infraphylum Archamoebae Cavalier-Smith 1993 stat. n. 1998
Class Archamoebea Cavalier-Smith 1983 stat. n. 2004
Family Tricholimacidae Cavalier-Smith 2013
Family Endamoebidae Calkins 1926
Order Entamoebida Cavalier-Smith 1993
Order Pelobiontida Page 1976 emend. Cavalier Smith 1987
Infraphylum Semiconosia Cavalier-Smith 2013
Class Variosea Cavalier-Smith et al. 2004
Order ?Flamellidae Cavalier-Smith 2016
Order ?Holomastigida Lauterborn 1895 [Artodiscida Cavalier-Smith 2013]
Order Phalansteriida Hibberd 1983
Order Ramamoebida Cavalier-Smith 2016
Order Profiliida Kang et al. 2017 [Protosteliida Olive & Stoianovitch 1966 em. Shadwick & Spiegel 2012]
Order Fractovitellida Lahr et al. 2011 em. Kang et al. 2017
Superclass Mycetozoa de Bary, 1859 ex Rostafinski, 1873
Class Dictyostelea Hawksworth et al. 1983
Order Acytosteliales Baldauf, Sheikh & Thulin 2017
Order Dictyosteliales Lister 1909 em. Olive 1970
Class Ceratiomyxomycetes Hawksworth, Sutton & Ainsworth 1983
Order Protosporangiida Shadwick & Spiegel 2012
Order Ceratiomyxida Martin 1961 ex Farr & Alexopoulos
Class Myxomycetes Link 1833 em. Haeckel 1866 Subclass Lucisporomycetidae Leontyev et al. 2019
Superorder Cribrarianae Leontyev 2015
Order Cribrariales Macbr. 1922
Superorder Trichianae Leontyev 2015
Order Reticulariales Leontyev 2015
Order Liceales Jahn 1928
Order Trichiales Macbride 1922
Subclass Columellomycetidae Leontyev et al. 2019
Order ?Echinosteliopsidales Shchepin et al.
Superorder Echinostelianae Leontyev 2015
Order Echinosteliales Martin 1961
Superorder Stemonitanae Leontyev 2015 [Fuscisporida Cavalier-Smith 2012]
Order Clastodermatales Leontyev 2015
Order Meridermatales Leontyev 2015
Order Stemonitales Macbride 1922
Order Physarales Macbride 1922
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The Cryogenian (from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
Cryogenian was the time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth").
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The Cryogenian (from Ancient Greek: κρύος, romanized: krýos, meaning "cold" and γένεσις, romanized: génesis, meaning "birth") is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.
Cryogenian was the time of drastic biosphere changes. After the previous Boring Billion years of stability, at the beginning of Cryogenian the severe Sturtian glaciation began, freezing the entire Earth in a planetary state known as a Snowball Earth. After 70 million years it ended, but was quickly followed by the Marinoan glaciation, which was also a global event. These events are the subject of much scientific controversy specifically over whether these glaciations covered the entire planet or a band of open sea survived near the equator (termed "slushball Earth").
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Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. As of 2022, 2.16 million living animal species have been described—of which around 1.05 million are insects, over 85,000 are molluscs, and around 65,000 are vertebrates—but it has been estimated there are around 7.77 million animal species in total. Animals range in length from 8.5 micrometres (0.00033 in) to 33.6 metres (110 ft). They have complex interactions with each other and their environments, forming intricate food webs. The scientific study of animals is known as zoology.
Most living animal species are in Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes, containing animals such as nematodes, arthropods, flatworms, annelids and molluscs, and the deuterostomes, containing the echinoderms and the chordates, the latter including the vertebrates. Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion, which began around 539 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago.
Historically, Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between taxa.
Humans make use of many animal species, such as for food (including meat, milk, and eggs), for materials (such as leather and wool), as pets, and as working animals including for transport. Dogs have been used in hunting, as have birds of prey, while many terrestrial and aquatic animals were hunted for sports. Nonhuman animals have appeared in art from the earliest times and are featured in mythology and religion.History of classification
In the classical era, Aristotle divided animals, based on his own observations, into those with blood (roughly, the vertebrates) and those without. The animals were then arranged on a scale from man (with blood, 2 legs, rational soul) down through the live-bearing tetrapods (with blood, 4 legs, sensitive soul) and other groups such as crustaceans (no blood, many legs, sensitive soul) down to spontaneously generating creatures like sponges (no blood, no legs, vegetable soul). Aristotle was uncertain whether sponges were animals, which in his system ought to have sensation, appetite, and locomotion, or plants, which did not: he knew that sponges could sense touch, and would contract if about to be pulled off their rocks, but that they were rooted like plants and never moved about.In 1758, Carl Linnaeus created the first hierarchical classification in his Systema Naturae. In his original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, the Chordata, while his Insecta (which included the crustaceans and arachnids) and Vermes have been renamed or broken up. The process was begun in 1793 by Jean-Baptiste de Lamarck, who called the Vermes une espèce de chaos (a chaotic mess) and split the group into three new phyla: worms, echinoderms, and polyps (which contained corals and jellyfish). By 1809, in his Philosophie Zoologique, Lamarck had created 9 phyla apart from vertebrates (where he still had 4 phyla: mammals, birds, reptiles, and fish) and molluscs, namely cirripedes, annelids, crustaceans, arachnids, insects, worms, radiates, polyps, and infusorians.In his 1817 Le Règne Animal, Georges Cuvier used comparative anatomy to group the animals into four embranchements ("branches" with different body plans, roughly corresponding to phyla), namely vertebrates, molluscs, articulated animals (arthropods and annelids), and zoophytes (radiata) (echinoderms, cnidaria and other forms). This division into four was followed by the embryologist Karl Ernst von Baer in 1828, the zoologist Louis Agassiz in 1857, and the comparative anatomist Richard Owen in 1860.In 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms: Metazoa (multicellular animals, with five phyla: coelenterates, echinoderms, articulates, molluscs, and vertebrates) and Protozoa (single-celled animals), including a sixth animal phylum, sponges. The protozoa were later moved to the former kingdom Protista, leaving only the Metazoa as a synonym of Animalia.
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Characteristics
Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular. Unlike plants and algae, which produce their own nutrients, animals are heterotrophic, feeding on organic material and digesting it internally. With very few exceptions, animals respire aerobically. All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle, but some animals, such as sponges, corals, mussels, and barnacles, later become sessile. The blastula is a stage in embryonic development that is unique to animals, allowing cells to be differentiated into specialised tissues and organs.
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] |
The Ediacaran Period ( ee-dee-AK-ər-ən, ed-ee-) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.
The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.
Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E.
The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, which is represented by now-extinct relatively simple animal phyla such as Proarticulata (bilaterians with articulation including Dickinsonia and Spriggina), Petalonamae (sea pen-like animals including Charnia), Disc-shaped forms (radial-shaped animals including Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry including Tribrachidium). Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago. Some modern groups of animals also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha. Mollusc-like Kimberella also lived during the Ediacaran. Fossilized organisms with shells or skeletons were yet to evolve in the Cambrian, the superseding period of the Phanerozoic eon.
The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations. The Shuram excursion also occurred during this period, but its glacial origin is unlikely.
|
followed by
| 17 |
[
"succeeded by",
"later followed by",
"came after"
] | null | null |
[
"Ediacaran",
"part of",
"Neoproterozoic"
] |
Upper and lower boundaries
The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum (Seilacher, 1955)).Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a "cap carbonate", because it caps glacial deposits.
This bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower global boundary stratotype section (GSSP) of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.
The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossil Treptichnus pedum (Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.
Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and ichnofossils are disputable.Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation) and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere in the world.
The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ l3Ccarb in the upper layer of the ocean.Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram Formation that is clearly away from any glacial evidence strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events. Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
|
part of
| 15 |
[
"a component of",
"a constituent of",
"an element of",
"a fragment of",
"a portion of"
] | null | null |
[
"Ediacaran",
"instance of",
"period"
] |
Upper and lower boundaries
The Ediacaran Period (c. 635–538.8 Mya) represents the time from the end of global Marinoan glaciation to the first appearance worldwide of somewhat complicated trace fossils (Treptichnus pedum (Seilacher, 1955)).Although the Ediacaran Period does contain soft-bodied fossils, it is unusual in comparison to later periods because its beginning is not defined by a change in the fossil record. Rather, the beginning is defined at the base of a chemically distinctive carbonate layer that is referred to as a "cap carbonate", because it caps glacial deposits.
This bed is characterized by an unusual depletion of 13C that indicates a sudden climatic change at the end of the Marinoan ice age. The lower global boundary stratotype section (GSSP) of the Ediacaran is at the base of the cap carbonate (Nuccaleena Formation), immediately above the Elatina diamictite in the Enorama Creek section, Brachina Gorge, Flinders Ranges, South Australia.
The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossil Treptichnus pedum (Seilacher, 1955). In the history of stratigraphy it was the first case of usage of bioturbations for the System boundary definition.
Nevertheless, the definitions of the lower and upper boundaries of the Ediacaran on the basis of chemostratigraphy and ichnofossils are disputable.Cap carbonates generally have a restricted geographic distribution (due to specific conditions of their precipitation) and usually siliciclastic sediments laterally replace the cap carbonates in a rather short distance but cap carbonates do not occur above every tillite elsewhere in the world.
The C-isotope chemostratigraphic characteristics obtained for contemporaneous cap carbonates in different parts of the world may be variable in a wide range owing to different degrees of secondary alteration of carbonates, dissimilar criteria used for selection of the least altered samples, and, as far as the C-isotope data are concerned, due to primary lateral variations of δ l3Ccarb in the upper layer of the ocean.Furthermore, Oman presents in its stratigraphic record a large negative carbon isotope excursion, within the Shuram Formation that is clearly away from any glacial evidence strongly questioning systematic association of negative δ l3Ccarb excursion and glacial events. Also, the Shuram excursion is prolonged and is estimated to last for ~9.0 Myrs.As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky, because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the level of T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"Ediacaran",
"named after",
"Ediacara Hills"
] |
The Ediacaran Period ( ee-dee-AK-ər-ən, ed-ee-) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.
The Ediacaran Period's status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it the first new geological period declared in 120 years.
Although the period takes its name from the Ediacara Hills where geologist Reg Sprigg first discovered fossils of the eponymous Ediacaran biota in 1946, the type section is located in the bed of the Enorama Creek within Brachina Gorge in the Flinders Ranges of South Australia, at 31°19′53.8″S 138°38′0.1″E.
The Ediacaran marks the first appearance of widespread multicellular fauna following the end of Snowball Earth glaciation events, the so-called Ediacaran biota, which is represented by now-extinct relatively simple animal phyla such as Proarticulata (bilaterians with articulation including Dickinsonia and Spriggina), Petalonamae (sea pen-like animals including Charnia), Disc-shaped forms (radial-shaped animals including Cyclomedusa) and Trilobozoa (animals with tri-radial symmetry including Tribrachidium). Most of those organisms appeared during or after the Avalon explosion event 575 million years ago and died out during an End-Ediacaran extinction event 539 million years ago. Some modern groups of animals also appeared during this period, including cnidarians and early bilaterians such as Xenacoelomorpha. Mollusc-like Kimberella also lived during the Ediacaran. Fossilized organisms with shells or skeletons were yet to evolve in the Cambrian, the superseding period of the Phanerozoic eon.
The supercontinent Pannotia formed and broke apart by the end of the period. The Ediacaran also witnessed several glaciation events, such as the Gaskiers and Baykonurian glaciations. The Shuram excursion also occurred during this period, but its glacial origin is unlikely.
|
named after
| 11 |
[
"called after",
"named for",
"honored after",
"called for"
] | null | null |
[
"Ediacaran",
"different from",
"Vendian"
] |
Ediacaran and Vendian
The Ediacaran Period overlaps but is shorter than the Vendian Period (650 to 543 million years ago), a name that was earlier, in 1952, proposed by Russian geologist and paleontologist Boris Sokolov. The Vendian concept was formed stratigraphically top-down, and the lower boundary of the Cambrian became the upper boundary of the Vendian.Paleontological substantiation of this boundary was worked out separately for the siliciclastic basin (base of the Baltic Stage of the Eastern European Platform) and for the carbonate basin (base of the Tommotian stage of the Siberian Platform).
The lower boundary of the Vendian was suggested to be defined at the base of the Varanger (Laplandian) tillites.The Vendian in its type area consists of large subdivisions such as Laplandian, Redkino, Kotlin and Rovno regional stages with the globally traceable subdivisions and their boundaries, including its lower one.
The Redkino, Kotlin and Rovno regional stages have been substantiated in the type area of the Vendian on the basis of the abundant organic-walled microfossils, megascopic algae, metazoan body fossils and ichnofossils.The lower boundary of the Vendian could have a biostratigraphic substantiation as well taking into consideration the worldwide occurrence of the Pertatataka assemblage of giant acanthomorph acritarchs.Subdivisions
The Ediacaran Period is not yet formally subdivided, but a proposed scheme recognises an Upper Ediacaran whose base corresponds with the Gaskiers glaciation, a Terminal Ediacaran Stage starting around 550 million years ago, a preceding stage beginning around 557 Ma with the earliest widespread Ediacaran biota fossils; two proposed schemes differ on whether the lower strata should be divided into an Early and Middle Ediacaran or not, because it's not clear whether the Shuram excursion (which would divide the Early and Middle) is a separate event from the Gaskiers, or whether the two events are correlated.
|
different from
| 12 |
[
"not same as",
"not identical to",
"distinct from",
"separate from",
"unlike"
] | null | null |
[
"Ventogyrus",
"instance of",
"fossil taxon"
] |
Ventogyrus is an Ediacaran fossil found in the White Sea-Arkhangelsk region of Russia. It was first discovered in the Teska member of the Ust'-Pinega formation, in a thick lens of sandstone, originally sand dumped by storm waves that cut a deep channel through the shallow sea bottom where the organisms lived. Many individuals were preserved on top of each other, often torn or in distorted positions. As a result, it was originally thought to have had a "boat shaped" form and to have lived anchored in the sea floor. However, a nearby site discovered later by Mikhail Fedonkin yielded separate specimens which were beautifully preserved in an upright position and showed the internal anatomy.Ventogyrus is now believed to have lived on or above the sea floor, an egg-shaped organism made of three modules (like the sections of an orange), all connected to a central rod. This three-fold, or triradial, symmetry is not usually found in the living world today, but it is also seen in other Ediacarans. The whole organism was wrapped by an external membrane. Individual fossils are approximately 6 cm in diameter and 12 cm long.Fedonkin and Ivantsov suggested there was a stalk attached to the body of Ventogyrus. Specimens with an intact basal side show the presence of a triangular cross-section with a circular structure in the center. It is possible this is where a stalk may have attached. Such a structure could have tethered Ventogyrus to the sea floor, or hung down to stabilize its position in the water column. Unidentifiable fossil fragments that could have been the remains of stalks were associated with the specimens.Ventogyrus is unique among Ediacaran fossils because so many have been preserved in three dimensions. The quality of its complex anatomical preservation is also unique among Ediacarans. This preservation allows paleontologists to more accurately conceive of how it, and other species similar in morphology, lived in and interacted with its environment.Relationships
Paleontologists have suggested different affiliations for Ventogyrus. Some follow Dolf Seilacher's theory that Ediacarans including Ventogyrus are an extinct phylum, the Vendobionta, related to no other living things. Ventogyrus is unusual among organisms proposed as vendobionts because paleontologists have also suggested relationships with post-Ediacaran fossils, including Erytholus from the Cambrian. Fedonkin has suggested, based on details of internal anatomy, that Ventogyrus could have been the float organism of a siphonophore colony (living examples include the Portuguese Man O' War). This reconstruction would make it a member of the phylum Cnidaria, related to jellyfish and corals. He has also suggested it could be related to animals in the early Cambrian Small Shelly Fauna whose "shells" were internal body supports. Ivantsov considers it an early representative of the phylum Ctenophora, the comb jellies, an ancient group whose members resemble but are not related to jellyfish. Ventogyrus does not fall obviously within one of the main form taxa of Ediacarans, the rangeomorphs, the erniettomorphs, and the trilobozoans, but it is also not obviously a member of a known biological taxon. While there is better information about the form of the living organism for Ventogyrus than almost any other Ediacaran, there is currently no consensus on what it was. However, investigators agree it was an animal.
|
instance of
| 5 |
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"type of",
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[
"Orthogonium",
"instance of",
"fossil taxon"
] |
Orthogonium is a genus of Ediacaran fauna approximately 550-530 million years old. Because of its taphonomy and likeness to other Ediacaran fauna, and as well as to crinoids, paleontologists dispute its classification.Description
The fossil consists of 8 parallel rows of tubes, which are square in cross-section, lying parallel to bedding. These tubes are divided into sections, the longest preserved tube is 58 mm long with 28, mesh-like sections, each of which is 2 mm high and 3 mm wide. Each section is separated from adjacent sections by a defined groove. These square section tubes may represent original pneu structures that did not collapse during fossilization and were filled with sediment, preserving the three-dimensional form of the structure.The fossil resembles several others, particularly Ectenocrinus simplex. This comparison was made by Gürich, who compared the tubes to the likeness of the arms of the crinoids. Mikhail Fedonkin, classified O. parallelum as a quilted petalonam because of its unique preservation. “They resemble sand-filled rocks which were composed of several tubes, often constricted midway by a prominent surface, but what these structures represent is uncertain.” J. John Sepkoski classified Orthogonium as a member of the subphylum Medusae with sister taxa including Bonata, Inaria, and Bronicella.
|
instance of
| 5 |
[
"type of",
"example of",
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] | null | null |
[
"Ciliate",
"instance of",
"taxon"
] |
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group (although the peculiar Suctoria only have them for part of their life cycle) and are variously used in swimming, crawling, attachment, feeding, and sensation.
Ciliates are an important group of protists, common almost anywhere there is water—in lakes, ponds, oceans, rivers, and soils. About 4,500 unique free-living species have been described, and the potential number of extant species is estimated at 27,000–40,000. Included in this number are many ectosymbiotic and endosymbiotic species, as well as some obligate and opportunistic parasites. Ciliate species range in size from as little as 10 µm in some colpodeans to as much as 4 mm in length in some geleiids, and include some of the most morphologically complex protozoans.In most systems of taxonomy, "Ciliophora" is ranked as a phylum under any of several kingdoms, including Chromista, Protista or Protozoa. In some older systems of classification, such as the influential taxonomic works of Alfred Kahl, ciliated protozoa are placed within the class "Ciliata" (a term which can also refer to a genus of fish). In the taxonomic scheme endorsed by the International Society of Protistologists, which eliminates formal rank designations such as "phylum" and "class", "Ciliophora" is an unranked taxon within Alveolata.
|
instance of
| 5 |
[
"type of",
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] | null | null |
[
"Scyphozoa",
"instance of",
"taxon"
] |
Taxonomy
Although the Scyphozoa were formerly considered to include the animals now referred to as the classes Cubozoa and Staurozoa, they now include just three extant orders (two of which are in Discomedusae, a subclass of Scyphozoa). About 200 extant species are recognized at present, but the true diversity is likely to be at least 400 species.Class Scyphozoa
|
instance of
| 5 |
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"type of",
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] | null | null |
[
"Eoandromeda",
"instance of",
"fossil taxon"
] |
Eoandromeda is an Ediacaran organism consisting of eight radial spiral arms, and known from two taphonomic modes: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation of China,
where it is abundant.Affinity
The organism was first interpreted as a trace fossil, and has also been considered to represent an agglutinating foraminiferan. However, the discovery of the Chinese fossils, which have preserved organic matter, ruled out these interpretations, because the Burgess shale type preservation displayed required relatively robust organic material to start with. Its spiral form has also led to comparison with the fossil embryos also preserved in the Doushantuo formation; the exact purpose still remains out on this until intermediate forms are found.The organism bears a very superficial resemblance to echinoderms, ctenophores and to some of the other Ediacara biota, but it lacks sufficient physical characteristics to ascertain with any degree of certainty whether it is indeed an animal or not. If it is, it would be the earliest known fossil of an adult animal; and its anatomy is consistent with that expected from the earliest animals. However, it is not perfectly clear that it is an animal; algae, the dominant constituent of the Doushantuo biota, cannot be ruled out, except that Eoandromeda seems a little too complex.
|
instance of
| 5 |
[
"type of",
"example of",
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] | null | null |
[
"Parviscopa",
"instance of",
"fossil taxon"
] |
Description
Parviscopa Hofmann et al. 2008 is similar to other frondose forms. It has a stem and branches and can appear plant-like. Specimens are typically between 2-3 centimeters in length. Parviscopa is found at the Bonavista Peninsula in Newfoundland, Canada and has been assigned to the phylum Petalonamae Pflug 1972. It is similar to the genus Primocandelabrum, which is also found in the same region, but Parviscopa is smaller and has better defined branches and lacks a basal attachment disc.Significance
Parviscopa is unique because it does not have rangeomorph branching like many of the other Avalonian taxa. Although Parviscopa is a body fossil, it resembles many trace fossils. It has also not been resolved if Parviscopa actually belongs to Primocandelabrum or if it is its own separate genus (see Diversity). Primocandelabrum and Parviscopa do not resemble larger taxa, and they are both only a few centimeters in length.
|
instance of
| 5 |
[
"type of",
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"manifestation of",
"representation of"
] | null | null |
[
"Protostome",
"instance of",
"clade"
] |
Protostomia () is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia. Well known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them.
Together with the Deuterostomia and Xenacoelomorpha, these form the clade Bilateria, animals with bilateral symmetry, anteroposterior axis and three germ layers.Protostomy
In animals at least as complex as earthworms, the first phase in gut development involves the embryo forming a dent on one side (the blastopore) which deepens to become its digestive tube (the archenteron). In the sister-clade, the deuterostomes (lit. 'second-mouth'), the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes (from Greek πρωτο- prōto- 'first' + στόμα stóma 'mouth') were so named because it was once believed that in all cases the embryological dent formed the mouth while the anus was formed later, at the opening made by the other end of the gut.
It is now known that the fate of the blastopore among protostomes is extremely variable; while the evolutionary distinction between deuterostomes and protostomes remains valid, the descriptive accuracy of the name protostome is disputable.Protostome and deuterostome embryos differ in several other ways. Many protostomes (the Spiralia clade) undergo spiral cleavage during cell division instead of radial cleavage.
Spiral cleavage happens because the cells' division planes are angled to the polar major axis, instead of being parallel or perpendicular to it.
Another difference is that secondary body cavities (coeloms) generally form by schizocoely, where the coelom forms out of a solid mass of embryonic tissue splitting away from the rest, instead of by enterocoelic pouching, where the coelom would otherwise form out of in-folded gut walls.
|
instance of
| 5 |
[
"type of",
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] | null | null |
[
"Anthozoa",
"instance of",
"taxon"
] |
Diversity
The name "Anthozoa" comes from the Greek words άνθος (ánthos; "flower") and ζώα (zóa; "animals"), hence ανθόζωα (anthozoa) = "flower animals", a reference to the floral appearance of their perennial polyp stage.Anthozoans are exclusively marine, and include sea anemones, stony corals, soft corals, sea pens, sea fans and sea pansies. Anthozoa is the largest taxon of cnidarians; over six thousand solitary and colonial species have been described. They range in size from small individuals less than half a centimetre across to large colonies a metre or more in diameter. They include species with a wide range of colours and forms that build and enhance reef systems. Although reefs and shallow water environments exhibit a great array of species, there are in fact more species of coral living in deep water than in shallow, and many taxa have shifted during their evolutionary history from shallow to deep water and vice versa.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"Charnia",
"instance of",
"fossil taxon"
] |
Charnia is a genus of frond-like lifeforms belonging to the Ediacaran biota with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture (thus exhibiting glide reflection, or opposite isometry). The genus Charnia was named for Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found. Charnia is significant because it was the first Precambrian fossil to be recognized as such.
The living organism grew on the sea floor and is believed to have fed on nutrients in the water. Despite Charnia's fern-like appearance, it is not a photosynthetic plant or alga because the nature of the fossilbeds where specimens have been found implies that it originally lived in deep water, well below the photic zone where photosynthesis can occur.Diversity
Several Charnia species were described but only the type species C. masoni is considered valid. Some specimens of C. masoni were described as members of genus Rangea or a separate genus Glaessnerina:
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"Pambikalbae hasenohrae",
"instance of",
"taxon"
] |
Diversity
Pambikalbae is a monospecific genus, with only one known species, Pambikalbae hasenohrae.Discovery
Pambikalbae hasenohrae was discovered within a fossiliferous exposure on the Nilpena pastoral property in the Flinders Ranges in South Australia. Pamela Hasenohr, an amateur geologist, found and brought the Pambikalbae fossils to the attention of Richard Jenkins, a research associate of the South Australian Museum. Richard Jenkins and his associate Chris Nedin collected five Pambikalbae specimens from this exposure, and published their description of the genus in 2007. In this publication, they named the type species of the genus, P. hasenohrae, after Pamela Hasenohr.Distribution
Pambikalbae hasenohrae specimens have been found preserved in channel sandstones on the Nilpena pastoral property in the Flinders Ranges of South Australia. These sandstones occur directly below the Ediacaran Member of the Rawnsley Quartzite, a stratigraphic layer rich with Ediacaran fossils that was deposited during cycles of marine transgression.
|
instance of
| 5 |
[
"type of",
"example of",
"manifestation of",
"representation of"
] | null | null |
[
"Hiemalora",
"instance of",
"fossil taxon"
] |
Hiemalora is a fossil of the Ediacaran biota, reaching around 3 cm in diameter, which superficially resembles a sea anemone. The genus has a sack-like body with faint radiating lines originally interpreted as tentacles, but discovery of a frond-like structure seemingly attached to some Heimalora has added weight to a competing interpretation: that it represents the holdfast of a larger organism.In 2020, a new study was published that described nine different from the Indreelva member, Digermulen Peninsula, Finnmark (Arctic Norway). The specimens described in the paper have high degrees of variation between morphologies and within the specimens that are though to be of the same species. Some of the representative fossils from that paper either show multiple Aspidella-like structures on the same specimen, or a Primocandelabrum-like cone visible in one of the fossils. All of the examples of fossils in the publication were determined to most likely represent the species Hiemalora stellaris, however, one of the more poorly preserved specimens (D18-50) is thought to have been representative of Hiemalora pleiomorphus, although the latter of the species represented by the specimens does not show parallel ridges running along the poorly preserved central disc. A representative of H, stellaris might have represented a holdfast with a Primocandelabrum frond attached to it, which may further support the theory of Hiemalora being a holdfast for Primocandelabrum.This interpretation would stand against its original classification in the medusoid Cnidaria; it would also consign a once-popular hypothesis placing Hiemalora in the chondrophores, on the basis of its tentacle structure, to the dustbin. Studies testing the feasibility of hypothesis investigated the possibilities that such fragile tentacles could be preserved, and concluded that it would be very improbable — especially as many Hiemalora bearing beds also contain such fossils as Cyclomedusa, but do not preserve the tentacles on these organisms.Hiemalora has been identified in a wide range of facies and locations globally.
|
instance of
| 5 |
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"type of",
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