Relation between direction of shear and tropical cyclone formation

The direction of the vertical shear plays a large role in cyclogenesis, where easterly shear tends to enhance the formation of cylones and westerly shear tends to suppress it (Tuleya and Kurihara, 1981).

Internal waves are responsible for large transfers of energy across vast distances. Therefore, they play important roles in a wide array of atmospherical (and oceanic) processes, such as tropical cyclogenesis (TC). These waves are capable of depositing energy that was created far away in an already active region. This energy may manifest itself in the form of an easterly shear. Depending on the type of wave, there is evidence that some waves play an important role in triggering cyclogenesis.

  It has been known for decades that about half of the hurricanes in the
  North Atlantic form from African waves (e.g., Frank and Clark 1980),
  and there have been many studies of this type of genesis (e.g.,
  Carlson, 1969; Landsea, 1993; Thorncroft and Hodges, 2001; and
  others). Molinari and Vollaro (2000), Mal- oney and Hartmann (2001),
  Liebmann et al. (1994).

There are three main classes of equatorial internal waves to consider when it comes to TC. Namely, the MJO, equatorial Rossby (ER) waves and other large wavenumber, high frequency waves that propagate towards the west (mixed Rossby gravity waves). Note that equatorial Kelvin waves are thought to have little effect on cyclogenesis. This animation from NOAA shows the internal waves (as OLR anomalies) over a period of 40 days:

Specifically:

the MJO and ER waves produce easterly shear anomaly at the generation location, while the MJO tends to reduce westerly shear over the atlantic.

  the MJO enhances both the convergence and the low-level rotation at the genesis location. [...] shows a tendency for the MJO to cause easterly vertical shear anomalies at the genesis location in most basins, and this would tend to be favorable for storm formation.  [...] The ER waves also appear to enhance genesis by increasing both the
   large-scale rotation and convection, as in this band the storms form
   within the low-level cyclonic gyre and about two days after the wave’s
   convective anomaly first reaches the genesis point. The ER waves also
   cause significant easterly shear anomalies at the genesis locations in
   about half of the basins.

Basically, internal waves enhance the formation of cyclones by increasing the vorticity of the local flow.

References:

Anantha R. Aiyyer and Chris Thorncroft, 2006: Climatology of Vertical Wind Shear over the Tropical Atlantic. J. Climate, 19, 2969–2983.

Tuleya, Robert E., and Yoshio Kurihara. "A numerical study on the effects of environmental flow on tropical storm genesis." Monthly Weather Review 109.12 (1981): 2487-2506.

William M. Frank and Paul E. Roundy, 2006: The Role of Tropical Waves in Tropical Cyclogenesis. Mon. Wea. Rev., 134, 2397–2417.


What does 5,000,000 tonnes of CO2 look like?

The question is hard to give a definitive answer to, as it depends on the pressure at which the gas is kept in the tank. But to try to give an intuitive sense of how much gas this is, let's work out two things: Firstly, how big the box would be at atmospheric pressure; and secondly, how many standard gas bottles it would take.

At atmospheric pressure

The mass of one mole of CO2 is 44 grams. So 5 MT of CO2 is $\frac{5\times 10^{12}}{44} = 114\times 10^9$ moles of gas.

The ideal gas law tells us that

$PV = nRT$

where $P$ is pressure, $V$ is volume, $n$ is the number of moles of the gas, $R$ is a constant, and $T$ is the temperature in Kelvin. If we assume a pressure of 100,000 Pa (roughly atmospheric pressure) and a temperature of 300 K (roughly room temperature), then

$V = \frac{nRT}{P} = \frac{114 \times 10^9 \times 8.314 \times 300}{10^5} = 2.8\times 10^9$ m3.

That volume works out to a cube with sides of 1.4 km.

In gas bottles

A standard large CO2 bottle of the type that is familiar in the UK looks like the one on the right of this picture:

and according to BOC contains 34 kg of gas, at a pressure of up to 50 bar. So that's 29.4 cylinders per tonne or, to contain 5 million tonnes of CO2, 147 million of these cylinders.


How can the following equations for meandering rivers be theoretically obtained?

I'm gonna hazard a guess here: They can't. While I don't have any evidence for this claim, it seems likely that there are too many small-scale non-linear processes feeding in to the overall generation process to ever be able to sensibly derive any kind of analytical solution based on physical first-principles. I think that's what you're asking.

So, basically, these equations are an empirical model. The parameters don't have any relation to the physical processes that generated the meanders - they are just descriptions of the resultant shape. The generation process for a model like this is something along the lines of:

Inspect the data qualitatively
Come up with some potential models that could approximate what you're seeing. In this instance, sinusoidal and sequentially linked circles look like they might work.
For each model, apply and verify:

Attempt to fit the model to some of the data.
Apply the model to some of the rest of the data, and check it's performance (also, pay attention to parsimony).

Choose the model with the best performance as your model.
With your model, perform some analysis of the model fit (residual analysis, etc). If it looks like there are patterns in the residuals that could be reasonably modelled, go back to 2. and come up with some model variants.

As far as I can tell from the referenced paper, this is roughly the process that the authors used. The values of each of the parameters are basically empirically obtained, to allow the model to best fit the majority of the data.


how can a complete novice find ore?

You don't.

In addition to Fred's excellent answer regarding the legalities of the matter, I would add the following:

All of the easy stuff has already been found, and finding any more ore requires efforts beyond what you can do on your own.
Stuff that is easy to find now is commonly in old mines or old mine tailings. These are dangerous places to be in. There is risk of collapse, acid mine drainage, and a bunch of other nasty things.
Learning how to find "ore" regardless of the first two points requires proper education in geological sciences.
Smelting copper ore, as per your idea, is a bad bad bad idea. Copper ore is usually in the form of copper sulfides. You really don't want to breath sulfur-bearing gases while you're smelting the ore.

If you are interested in looking for minerals and such, as a resident of New South Wales I recommend you talk a look at this website:

https://www.resourcesandgeoscience.nsw.gov.au/miners-and-explorers/fossicking-in-nsw

It contains information and resources that might be useful to you.


Volcanic plumes and pyroclastic flows are two behaviours of basically the same thing. A volume of hot gasses and tephra (a.k.a. a mix of ash, pumice, and volcanic rocks of different sizes).

If the gas is hot enough and the tephra content is light enough the mix will be buoyant and it will rise as a volcanic plume. On the other hand if gas is too cold to support the plume, or the weight of the tephra is too heavy. It will collapse and rush downhill as a pyroclastic flow. That is referred to as a "Fountain collapse", and is the most common cause of pyroclastic flows.

That is why the are also referred as density or gravity currents.


Why is the Ocean water on the west Coast so cold comparing to the East coast?

This is a good overview of ocean surface currents, which includes a schematic like this one:

In the mid-latitudes, you get gyre circulations that move poleward along the eastern coasts of continents (the western edges of the ocean), bringing warm water. The water off the east coasts of these places is thus warmer than you would expect for that latitude. The return flow on the eastern edges of ocean basins (west coast of continents) brings cold water from poleward of that latitude.

There are a few things to note about this circulation, though, since that analysis applies to the mid-latitudes only. There are opposite gyres closer to the poles that make the east coasts much colder than expected. (Compare the Alaska current to the Labrador, which is off the east coast of Canada.) The circulation near the equator is a lot more complex and interesting, especially where it meets up with other gyres.

There are some strange and fascinating reasons why the circulation is the way it is, but that answer is the result of an entire oceanography course...


What is the vertical axis of this waveform shown in this tweeted IRIS GIF?

Answer 1

The horizontal axis is indeed time (don't forget units and note how long those periods are!). As for the vertical axis, I'm certain that this is displaying vertical (or 'Z' or 'V') displacement. Keep in mind - like you mention - that we are only looking at a 1-D picure of the data, but there are other perspectives we are missing! For example, how is the earth being displaced with respect to North-South and/or East/West directions?

Answer 2

The vertical blue line you reference indicates different seismic phases (or arrivals). For example, you list 'P' and 'PcP' - but there are many others! For example 'SKS', 'SKKS', etc. - see the hyperlink to understand this notation and the seismic waveforms they correspond to.

NOTE(1): For the term phase - be VERY careful with this word and the context I've applied it in. As is customary in geophysics, one word can refer to the same or different concepts. Read here for a good follow-up example of what I'm describing in terms of phase.

NOTE(2): Many seismograms like this will initially be displayed in the conventional NEV (or NEZ) or North-East-Vertical coordinate system . But, to optimize many kinds of analyses and displays, one needs to rotate (or transform) this system into another - LQT. Read here to understand what that means.

NOTE(3): How does one know or estimate seismic phases like these? You need an earth model! From the source location and at the instantaneous moment of when the seismic event occurs, a corresponding seismic wavefield is generated and travels throughout the earth - interacting with its fluid and/or elastic mediums - all the while responding to (or convolving) its complex, 3-D velocity (and density) structure. As the seismic wavefield passes through different mediums via refraction, reflection, dispersion,
attenuation, etc., it changes and subsequent various phases are produced and then recorded at a station. The phases - i.g. 'SKS', 'P', and many others - basically tell a story of how/where the wavefield changed, which is great for analyzing the crust, all sections of the mantle, and even the core!

*I've included a lot here but you've asked an outstanding question that you (and I) can really learn from!


tl;dr: The Earth receives 40,000 tons of dust from space every year, but looses 95,000 tons of Hydrogen and 1,600 tons of Helium every year as well. After all additional effects are balanced, the Earth looses about 50,000 tons a year.

It seems a similar question was asked in Astronomy Stack Exchange, and this short answer links to the BBC News article Who, What, Why: Is the Earth getting lighter? which answers this question.

There are factors that are causing Earth to both gain and lose mass over time, according to Dr Chris Smith, a medical microbiologist and broadcaster who tries to improve the public understanding of science.
Using some back-of-the-envelope-style calculations, Dr Smith, with help from physicist and Cambridge University colleague Dave Ansell, drew up a balance sheet of what's coming in, and what's going out. All figures are estimated.
By far the biggest contributor to the world's mass is the 40,000 tonnes of dust that is falling from space to Earth, says Dr Smith.

Surprisingly, General Relativistic effects of Global Warming is considered!

Nasa has calculated that the Earth is gaining energy due to rising temperatures. Dr Smith and his colleague Mr Ansell estimate this added energy increases the mass of Earth by a tiny amount - 160 tonnes.

Using $E=mc^2$ that works out to about $1.4 \times 10^{22}$ Joules/year or $4.6 \times 10^{14}$ Watts. That's about 3.6 Watts/meter^2 or about 0.3% of the total power coming from the Sun, so it does seem to be back-of-the-envelope-in-the ballpark correct!

But there is something else that is making the planet lose mass. Gases such as hydrogen are so light, they are escaping from the atmosphere.
"Physicists have shown that the Earth is losing about three kilograms of hydrogen gas every second. It's about 95,000 tonnes of hydrogen that the planet is losing every year.
"The other very light gas this is happening to is helium and there is much less of that around, so it's about 1,600 tonnes a year of helium that we lose."
So taking into account the gains and the losses, Dr Smith reckons the Earth is getting about 50,000 tonnes lighter a year, which is just less than half the gross weight of the Costa Concordia, the Italian cruise liner, that ran aground recently.


Is heavier bodies fall faster than lighter ones

The two stones will accelerate at the same rate due to gravity. This is usually attributed to Galileo although it was known before that - eg. John Dee was aware of it and didn't think it a new revelation.

So if the two stones have the same shape and size - ie. so aerodynamic effects are identical, they will fall at the same acceleration and speed.
There are plenty of experiments to demonstrate this, but perhaps one of the most well known was by one of the Apollo astronauts (the Moon being essentially airless has no aerodynamic effects).  The result can also be derived from Newton's Inverse Square Law of Gravity and his Second Law of Motion.

If I were you, I would forget about Aristotle when it comes to trying to understand the world around us. He didn't have any concept of forces, inertia, and momentum as we would understand it today. His concept of forces was provably wrong with knowledge available to him at the time.


This is a really bad question, because all three can lack fossils, or all three can have fossils. The definition of "minerals" is also a bit unclear, because fossils are also made out of minerals. I'll assume that by minerals they mean non-biogenic minerals. Let's go through each one of them:

  a clastic sedimentary rock

This rock will have minerals, because this is what is being transported. Usually quartz, feldspars, clays, heavy minerals, etc. But, it can also have fossils. Fossils can be transported as well, and it is not uncommon to find fossils in clastic sedimentary rocks. They are usually not intact, but still fossils nonetheless.

  a chemical sedimentary rock

This will have minerals, obviously. This might also have fossils: what if there were organisms around while the chemical rock formed? Could be fossils falling from above into a carbonate precipitate, or insects in an evaporite basin. However, this is probably the least likely rock to contain fossils. If you have to choose only one, this would be it (unfortunately).

  iii) a biochemical sedimentary rock

This sounds like an obvious one to contain fossils, but it may not be. What about limestones where all of the fossils were broken down to unrecognizable fragments of calcite? Also known as a micrite? This would be biogenic, but it wouldn't be clear what fossils are there.


Velocity from time and depth seismic images

Disclaimer: It a very crude way to do it.! Take it as the last resort.

It assumes that you know velocity for the shallower reflectors/layers. I will explain for one reflector and you can extend for deeper reflectors.

Step 1. You slice out the reflector event (in a trace) you want to find the velocity for.

Step 2. Take a correlation with the respective trace in other time/depth domain part and find the max correlation time/depth. Here you may assume this time corresponds to the respective depth so you get total travel time.

Step 3. At this point you know the interval velocities for layers at the shallower depth, so you can find out the interval velocity for this layer.

You start from the top and continue to bottom side. You may treat it as layer stripping.


European soil texture dataset according to USDA classification

After a lenghty unsuccessful search, I found an option to do my own mapping. There are global datasets with the percentages of clay, silt and loam available from the Land-Atmosphere Interaction Research Group at Sun Yat-sen University and I used the R soiltexture package for the classification. I ended up making a dataset covering my domain of interest in 2 km resolution. I attached my map and the original map mentioned in the question for comparison (some of the colours are a bit off, but they should more or less correspond to the same category in both images). If anyone is interested in this data, feel free to let me know. My custom mapping.

Original dataset from the European Soil Data Centre (ESDAC)


Is there any consensus of what caused the Lusi Mud Volcano eruptions in Indonesia?

No, there is no consensus.

In fact, there's quite a bit of debate about it — around the 2 causes you mentioned. To sum up the proposed triggers:

The eruption happened about 2 days after the 2006 Yogyakarta earthquake, which killed over 5000 people. Lupi et al (2013), Sawolo et al. (2011), and others including the Indonesian government, favour this as the trigger.
The eruption happened about 200 m away from Lapindo Brantas's Banjar Panji 1 exploration well. There were early signs of trouble in the well, which started when the earthquake happened. At the time, the incident was treated as a blow-out, relief wells were drilled, etc. Davies et al. (2011), and others, blame this.

Last year I blogged about Lusi. The first-order cause was not my focus (though I insinuated that I thought the well exploited a predisposition set up by the earthquake); I focused instead on the history of the event. But much of the controversy emerged in the comments, which are worth reading.

Rather than trying to synthesize everything into an elegant summary, I'll just point out two of the complications in all this:

The Lupi et al (2013) argument has serious flaws, because the authors misinterpreted the sonic (DT) log from the well. This was partly, but not completely, resolved by the corrigendum published in 2014. In a nutshell, the fast layer they argued for was a logging artifact.
There is a legal backdrop to the argument, which may not be compatible with an objective scientific debate. For the company, there is the question of liability and thus reparations, which could be expensive. For the government, there is the question of international financial relief, some of which is contingent on Lusi being a natural disaster.

The debate may not be satisfactorily resolved for some time. It seems to be one of those unhelpful debates where, to the participants at least, there is no uncertainty. My heuristic in such situations is to assume this means that "it's complicated".

References

Davies, R, S Mathias, R Swarbrick and M Tingay (2011). Probabilistic longevity estimate for the LUSI mud volcano, East Java. Journal of the Geological Society 168, 517–523. DOI 10.1144/0016-76492010-129.
Lupi, M, EH Saenger, F Fuchs and SA Miller (2013). Lusi mud eruption triggered by geometric focusing of seismic waves. Nature Geoscience 6, 642–646 (2013) DOI 10.1038/ngeo1884.
Sawolo, N, E Sutriono, B Istadi, A Darmoyo (2009). The LUSI mud volcano triggering controversy: was it caused by drilling? Marine & Petroleum Geology 26 (9), 1766–1784. DOI 10.1016/j.marpetgeo.2009.04.002.


Glowing Orange lakes seen from airplane at night

The orange lakes are most likely tailing dams, also known as tailings storing facilities given that they located near an open pit iron ore mine.

Once iron ore has been mined it is usually sent to a processing plant to increase the grade (amount) of iron in the product the mine exports. It does this by removing as much waste material as possible. Sometimes the waste is low grade iron ore (very low concentration of iron);.

Usually the ore is crushed, ground and treated chemically. What is deemed as waste (tailings) is sent/dumped to a tailings dam. There will always be an amount of unrecoverable iron in the tailings which will give the tailings a reddish color. Low Moon angles may accentuate the red or orange coloring.


If I was to tunnel straight through a mountain, what kind of rock would I find?

As Gary mentioned, it really depends on particular context for your mountain. How did it form? Is it volcanic in nature? Or maybe just old rocks being uplifted by some episode of compression.

On average, Earth's crust is pretty much granite. So chances are that you will find that inside your mountain. That wouldn't be a bad assumption. Granites form by cooling magma slowly, so most volcanic-type mountains are made of granite or something similar. For example, the Andes (below) are made of fine-grained Andesite near the surface and Diorite (Andesite's coarse-grained version, which is similar to Granite, but not quite) at depth.

In the case of cooling magma to form rocks, the slower the cooling, the larger the crystals will be. So rocks that cooled near the surface, will be composed of tiny crystals while rocks that cooled deeper will have larger crystals.

You could argue for more exotic rock types but that would imply a slightly more complex geological history (which is totally possible). For example, you could have uplifted a huge package of sedimentary rocks without any volcanism involved. Or you could have simply eroded everything around leaving large rock packages like the Venezuelan Tepuis (below).

In general, the rocks deep inside a mountain (or simply super old rocks) have also undergone a lot of compression, so sedimentary rocks will be unlikely as you would have converted them into metamorphic rocks, e.g. limestones would be marble, sandstones would be quartzites (like the Tepuis), shales would be slates (or schists, etc.), etc.

Similarly, metamorphic rocks that have undergone a higher degree of compressional and thermal stress (i.e. deeper in the mountain) will grow larger crystals.

Of course, like anything in geology, other complex scenarios do exist where these rules of thumb don't work. But in general, this should get you started.

Anyway, hope that helps.


Why are there no mountains higher than ~10 km?

The reason mountains are higher on Mars than on Earth is the lower gravity on Mars, which is only one third of Earth gravity. Mountains are very heavy things, and on Earth the forces that build them have to fight against gravity, which is constantly trying to drag them down. For the same reason, small asteroids are usually not spherical, because they don't have enough gravity to even out the bumps, but when they get to about the size of Ceres, which is 500 miles in diameter, they do. Ceres is spherical. Mountains like Mauna Kea which have a large part under water don't count, because although mountains are heavy things they still have buoyancy and the sea is taking part of their weight. Venus has slightly less gravity than Earth, but because of the enormous heat is also more plastic, so this would mitigate against the building of very high mountains.


Please help in understanding redox buffers

First let me start by saying that redox buffers are a made-up thing. All these QFM (actually FMQ) or NNO or other abbreviations don't exist in nature. They were developed as a way to "cheat" in experiments to get the desired Fe(II)/Fe(III) ratio, and later extended for more uses. High temperature and pressure experiments are permeable to hydrogen: it just goes through the experimental capsule. Depending on the direction of diffusion, it can either oxidise or reduce the contents of the capsule, changing the desired Fe(II)/Fe(III) ratio. Buffers "force" a certain oxygen fugacity. In reality, redox (or not) is buffered by a variety of reactions that we may not even know exist.

  partial pressure (fugacity) of an element such as oxygen

In the deep Earth, there is no free O2 gas phase, so it doesn't make sense anymore to talk about the "partial pressure". But the oxygen fugacity controls the reactions involved electron transfer (i.e. buffers).

  how oxygen fugacity influences mineral crystallization

In general, higher oxygen fugacity means there's a higher ratio of Fe3+ to Fe2+. This is particularly true in melts. So a melt with lots of Fe3+ will crystallise magnetite (for example) whereas a reduced melt with little Fe3+ will not. This is one of the differences between tholeiitic and calc-alkaline differentiation trends. Calc-alkaline melts are oxidised, so they crystallise magnetite early. Therefore, they never reach high Fe contents. Tholeiitic melts re reduced, and magnetite does not crystallise until very late, so it is possible for them to reach high Fe contents.

This is also important for sulfur. Will a volcano erupt SO2 or H2S? It all depends on the oxygen fugacity of the system.

I will also add that the bulk amount of Fe3+ and Fe2+ does not directly tell you where a rock is oxidised or not (with respect to oxygen fugacity). For example, a rock with 1% hematite, 98% enstatite and 1% magnetite will have more bulk Fe2+ than a rock with 50% magnetite, 49% quartz and 1% fayalite. But, the former is at the HM buffer while the latter is at the FMQ buffer (reduced).

I highly recommend reading this (preferably more than once):

Frost, B. R. (1991). "Introduction to oxygen fugacity and its petrologic importance." Reviews in Mineralogy and Geochemistry 25: 1-10.


What are the ramifications to life on Earth when the Earth's magnetic poles switch?

While this does not directly answer the question, these two ideas are relevant: Rare Earth hypothesis and Mediocrity principle.

More focused to the question, This letter to nature discusses the purposed link between evolution/mutation rate during of life and magnetic pole reversal periods. You see, when the magnetic fields reversed, it widely thought that it occurs over a period on the order of 1 - 10,000 years. During this reversal, the intensity of the magnetic field degrades to 0, and then increases from there in a reversed polarity. It is not a contentious position that during these field reversals the mutation rate (not sure about speciation rate) dramatically increases.


Are AO-GCMs sensitive enough to take large lakes into account?

The resolution of AO-GCM are not high enough to include lake model in their code, at least as far as I can remember (looking at google scholar, I have not found anything related to lake model in AOGCM).

However, lake model are implemented (and operational) in regional climate model (RCM), such as CRCM5 (Canadian Regional Climate Model v5). See for example Martynov et al. (2012), where they describe the results of implementing lake model in a 45km resolution simulations. On that note, I think that until AOGCM (and now the Earth System Models, which implement carbone cycle) goes to resolution close to 50km, they won't adopt massively such lake models.

From Martynov et al. (2012)

"The  presence  of  lakes  influences  mostly  the  lake-rich region of the Canadian Shield by altering the low-level  air  temperature,  humidity  and  precipitation.  The influence of lakes on the precipitation is most significant over   the   Laurentian   Great   Lakes   and   within   the distance  of  200-300  km  downstream  of  these  lakes,
especially  with  open  water  on  lakes  in  wintertime.  The patterns of enhanced precipitation correspond to regions of the well-known lake effect snow on downwind coasts of  the  Great  Lakes."

Since the effect is rather regional, I suspect that other climate processes are more important for the AOGCM modellers.

Citations

Martynov, Andrey, Laxmi Sushama, René Laprise, Katja Winger, and Bernard Dugas. 2012. “Interactive Lakes in the Canadian Regional Climate Model, Version 5: The Role of Lakes in the Regional Climate of North America.” Tellus A; Vol 64 (2012), February. http://www.tellusa.net/index.php/tellusa/article/view/16226.

On ResearchGate: https://www.researchgate.net/publication/234872039_Interactive_Lakes_in_the_Canadian_Regional_Climate_Model_version_5_The_Role_of_Lakes_in_the_Regional_Climate_of_North_America


How are the ZNE, ZRT and LQT coordinate systems defined?

Z depends upon convention, but in geophysics we typically use Z=positive downward. R is radial and the positive direction is defined in the direction FROM the source TOWARD the receiver. T polarity can be determined from the right-hand rule once you have Z and R.

For reference, this is the based on the convention for polarity as described by Aki and Richards (1980).


You might get a lava seepage, but I doubt it. The cross-sectional area of a borehole is small compared to the total cross sectional area of fractures that are there already. Note that volcanoes bulge quite markedly due to lava up-welling and deformation due to magma pressure, so the volcano is invariably well fractured. A small hole is likely to fill up with magma rapidly, which would cool and solidify against the country rock, thereby plugging the hole - unless the borehole was very close to a gassy magma chamber. However, there might be exceptions in that very small fraction of volcanoes that are of the 'Plinian' type, in which exceptionally high gas pressures can occur. But then, nobody in their right mind would drill into a potentially Plinian type of volcano!


In simple big picture terms, Sediments were deposited first from the bottom upwards (as you understand). Then the area was uplifted and the river eroded from the top down.

Most erosion is from the top down (there are scenarios such as dissolution and caves which are relatively rare exceptions). So here in Texas we find a large amount of the center of the state was covered with Cretaceous sediments which have since eroded away. We see signs of this from "outliers" - basically remnant caps of Cretaceous on the tops of hills.

As I say this is big picture viewpoint. The very bottom of the Grand Canyon has metamorphic rocks. And sedimentation will not have been continuous. There are gaps from erosion, uplift, etc. But yes the bottom is about 2 billion years old, and erosion of the canyon itself is "relatively" recent.


Seeking climate and related sciences textbook recommendations

There are loads of books. I will refer you to one of my previous answers which can apply to the meteorological aspects of climate. An additional classic for climate is Physics of Climate by Peixoto and Oort.


Which component in a 3-component Sp receiver function is the actual Sp RF?

I am not sure I clearly understand the question, but here is a quote from the paper that I looked at a while ago about S Receiver Functions.

From: Yuan, Xiaohui, Rainer Kind, Xueqing Li, and Rongjiang Wang. " The S Receiver Functions: Synthetics and Data Example ." Geophysical Journal International 165.2 (May, 2006): 555-564:

"Here we briefly summarize the processing steps for generating S receiver functions. The ZNE-component seismograms of S and SKS waves are rotated firstly into the ZRT system with the back azimuth determined by locations of the receiver and earthquake. The ZRT components are further ro-tated into the P-SV-SH system with the incidence angle determined by minimizing the amplitudes at time of S/SKS arrival on the P component. Waveforms are visually selected to avoid the confusing of S and SKS phases. Data with strong interference of S and SKS are excluded. A window of S/SKS waves on the SV component is deconvolved from the P component for source equalization. For direct comparison with the P receiver functions, we need to reverse the time axis as well as the amplitudes of the S receiver functions.Move-out correction is then applied for all the PRFs, SRFs and SKSRFs, with a reference slowness of 6.4 s deg−1 and the IASP91 model as reference."

Does this help?


Is there a name for these "pouring" clouds?

The term used by the American Meteorological Society is orographic fog. A perhaps more descriptive name is "orographic waterfall cloud".

Prevailing winds can force air to flow upwards over rising terrain. The rising air cools more or less adiabatically, and this can in turn result in clouds. The nature of the orographic clouds (orographic: "related to mountains") that result vary greatly.

In arid regions, orographic clouds can form lenticular clouds that look amazingly like UFOs (three links). Unstable conditions can result in wave clouds, where an obstruction causes a cloud after cloud after cloud downwind of the obstruction. Even icebergs can cause wave clouds. Another form of orographic cloud is a banner cloud, where a cloud flies like a banner downwind of a mountain:

Source: https://commons.wikimedia.org/wiki/File:Banner_clouds.jpg . Copyright Zacharie Grossen, license CC BY-SA 3.0

This is getting closer to an orographic fog. Climbers on the Matterhorn oftentimes experience that cloud, firsthand. Even closer to home is Table Mountain near Cape Town, South Africa.

Source: https://commons.wikimedia.org/wiki/File:Cape_Town,_Table_Mountain,_Table_Cloth.jpg. Copyright KodachromeFan, license CC BY-SA 3.0

This is an orographic fog. (Table Mountain can also create some rather spectacular lenticular clouds.) Another example of an orographic fog is detailed in the article "Waterfall-like Orographic Clouds".

The conditions needed to form an orographic fog include

Prevailing winds that force air to blow upwards over an obstruction, with the orographic fog flowing downwind from the obstruction.
The flowing air must be sufficiently humid. Without this condition, you might see a very cool looking lenticular cloud, but you won't see a banner cloud or an orographic fog.
The flowing air must be sufficiently cool. Humid air at the same pressure and temperature of arid air is less dense than is that arid air. The flowing humid air has to be fairly cool for the flow to be downward downwind of the obstruction.
The flow has to be fairly slow (low Reynolds number) and uniform (low Froude number). Otherwise, a wave cloud or banner cloud will result.


How many times in total has Earth formed a super continent?

According to a review by Nance & Murphy (2013), there are five known supercontinents, from the most recent to the most ancient:

Pangea (of course)
Pannotia (though it depends on how you define supercontinent), ca. 600 Ma
Rodinia, breakup at ca. 750 Ma (see e. g. Torsvik, 2003)
Columbia (also called Nuna), ca. 1.6 Ga
Kenorland, ca. 2.7 Ga

Some additional ones such as Vaalbara in the Archean are still mostly speculative.


What happens in the upper air when the altitude of the tropopause changes?

Short answer: I think the difference in the 2 soundings can be mostly explained by moving from one air mass (low pressure, relatively humid) to another (high pressure,  relatively dry) which also increases the tropopause height.

One thing you have to realize is that radiosoundings never provide a perfect vertical profile moving straight into the atmosphere with respect to the location you start your radiosounding but rather move with the wind. One thing that is obvious from your radiosoundings is that there is a strong backing of the wind, visible in the layer from the surface up to 500 hPa but most prominent in the layer from the surface up to +/- 700 hPa. Also, the wind speed seems to decrease slightly. These conditions imply that your location of the radiosounding near the height of the tropopause (may) have shifted significantly.

In combination with the temporal difference of 12 hours this may explain the discrepancy. From the first sounding to the second we also see advection of relatively warm, dry air in the 800-400 hPa layer. We find that temperatures go up, and the differnce between temperature and dry bulb temperature seems to increase. We also find that the surface pressure goes up, indicating a regime with higher pressure.

Still, we can not be certain that these conditions specifically apply for your radiosounding location. We can conclude that the above findings are speficially true for the pathway of the radiosonde.


How does Earth's heat escape to space?

TL;DR: By the exact same method heat from the Sun escapes into space. Electromagnetic radiation does not require a medium. In fact, electromagnetic radiation works best in a vacuum; no medium is required. Intervening matter has an annoying tendency to absorb electromagnetic radiation. That absorption, in a nutshell, is the greenhouse gas effect.

Earth's heat escapes into space via a complex set of processes. One is convection. Eagles, hawks, and other birds use those rising thermals to get a free ride to altitude. A second mechanism is latent heat. Evaporation of water is an endothermic process, meaning it absorbs energy from the surroundings (this is why sweating keeps you cool). Condensation is an exothermic process. While falling rain cools the surface, the net transfer is upward.

Those rising columns of warm air can only go so high; they only rarely cross the tropopause (the boundary between the troposphere and stratosphere), and that is only in the case extremely unstable of conditions. Latent heat, along with birds, ride those rising columns of air. This brings up a third and the ultimate mechanism by which the Earth's heat escapes into space, which is electromagnetic radiation.

Every object, including the Earth's surface, absorbs and radiates heat electromagnetically. The atmosphere does the same. The atmosphere absorbs most of the electromagnetic radiation emitted by the Earth's surface. (I qualified that with "most" because there is a small window in the thermal infrared that goes directly into space, at least when there aren't clouds.) This absorbed radiation is quickly re-emitted as thermal radiation, but in a random direction.

The heat carried upward by thermals, by latent heat, and by surface radiation eventually does make its way into space as electromagnetic radiation.


What ozone depleting chemicals can salt produce?

A study presented in the Science Daily article (based on a Science article), Study: Sea Salt Seasons Chemical Brew That Destroys Arctic Ozone (Purdue University, 2001) could serve as an analogue to salt induced ozone depletion.

Sea salt, in particular, compounds formed from the constituent chlorine, bromine (and fluorine) found in most salts have been identified as ozone depletors - researchers have found that the sea salt in the Arctic containing these ions cause a seasonal thinning in the Arctic.  With a large concentration of salt in the strata, as found in the region of the Siberian Traps, it is not inconceivable to assume that large quantities of chlorine and bromine were released in the atmosphere.

Quantitatively, according to the article Magnitude and consequences of volatile release from the Siberian Traps (Black et al. 2012), the actual amount released was in the order of approximately ~3400–8700 Gt chlorine, of which a good proportion was, according to the article, assimilated into the magma from melting of the evaporite, salt and sedimentary rocks.  Also postulated by Environmental mutagenesis during the end-Permian ecological crisis (Visscher et al. 2004) was that the size of the Siberian volcanics caused the assimilation of volumnous organics and halogen based deposits (including salts).

These hypotheses are supported by experiments reported in the article Contact metamorphism, halocarbons, and environmental
crises of the past (Svenson et al. 2009), where rock salt from Siberia was heated to 275C released ozone depleting halocarbons such as methyl chloride (CH3Cl) and methyl bromide (CH3Br).

In general, considering the most common salt is sodium chloride (NaCl), once dissolved, the chloride ion (Cl-) is very reactive, and forms several ozone depleting compounds (such as the halocarbon examples above), and chlorine itself can react to 'tear apart' ozone itself, as shown in the diagram below:

Image Source: NOAA

The example used in the image above are manmade CFC's (chlorofluorocarbons), however, it can be applied to any halocarbon or for chlorine itself from step 3 onwards.

In conclusion, any halogen (particularly F, Cl, Br) based salt are potential ozone depletors, due to the reactivity of the halogen ions.  Especially Cl due to how common NaCl salt is, the Cl (and other halogens) can react with other chemicals that may be present also providing ozone depleting chemicals.  So, given the amount of salt that the Siberian Traps that would have heated up, the chances of a fairly large effect on the ozone layer at the time are pretty good.


Yes, there is some amount of circular reasoning in the statement: "geologist date rocks by the fossils they contain and date fossils by the rocks in which they are found".

However, that statement does not fully describe how geologists date rocks or fossils. Dating rocks by fossils is a branch of geology called "biostratigraphy". This is a non-absolute and a relative method of dating. You know that one fossils is younger than another, so you can be sure that one rock is younger than another rock given that they have those fossils, respectively. How old are they exactly? Based on biostratigraphy alone, this is an unknown.

The problem is solved using geochronology. Using radioactive decay to accurately and precisely date rocks. This is independent of fossils, but requires that the rock have to be dateable. This means that you need some kind of volcanic material (among other things) interbedded with the fossil bearing rocks. When you do that - you can be sure that a certain fossil formed at some exact point in time. Let's say 100 million years ago. Then you can use that knowledge to assign an age to rocks containing similar fossils where you do not have any rocks that you can date.

That said, new technological advances allow us to directly date fossils. One of the methods is using the Lu-Hf or U-Th-Pb systems on apatite - a mineral that forms teeth and bones. In cases where this method has been applied it showed that biostratigraphy actually works (unsurprisingly and to the dismay of creationists).


Why do most opal deposits occur in Australia?

A recent study published in the Australian Journal of Earth Sciences, Opalisation of the Great Artesian Basin (central Australia): an Australian story with a Martian twist (Rey, 2013). The study makes the assertion that a unique set of geological conditions existed during the Cretaceous era that led to the relative abundance of opals in Central Australia. Rey proposes a 'redox model' of opal formation to account for the great relative abundance of the precious stone in Australia.

An important aspect to note is that just about all opal deposits occur either in or on the periphery of the Great Artesian Basin, as can be seen in the map below:

Image Source and brief information of opal mining centres: The National Opal Collection

The conditions around the opal field part of the Artesian Basin during the Cretaceous, according to Rey (2013) were:

From about 130 to 93 million years ago, The Great Artesian Basin was flooded by what is known as the Eromanga Sea, this was a cold, shallow, largely stagnant waterway that was poorly connected to the open ocean.
The Eromanga Sea served as a 'sink' for volcaniclastic sediments eroded from orogenic volcanic sources on the Pacific margin of Gondwana.

Rey describes how the iron- and organic- rich sediments contributed to an anoxic seafloor environment that became rich in pyrite, ferrous iron, feldspar and volcaniclasts, but virtually no carbonates.

At the end of the Cretaceous and into the early Palaeogene (from about 93 to 60 million ears ago), the region experienced slow uplift, erosion and denudation, as well as subsequent sea regression; this, according to Rey, caused an acidic oxidation of the Eromanga Sea deposits as oxic fluids perculated through faults, some trapped by clay deposits - these are where the opal deposits have been found.  Further deposition in the Palaeocene and Eocene provided protection from further erosion.

In summary, Rey notes 5 aspects unique to the geological history of the Great Artesian Basin that has resulted in the great relative abundance of opal:

Large scale organic matter-rich, iron-rich volcaniclastic sediments
The depositional environment to be anoxic
negligible carbonates
sea regression driving oxidative weathering
stable landscape to preserve opal from erosion and to prevent its transformation into quartz via burial

The connection to Mars in the title is based on recent observations by NASA of opaline minerals found on the Martian surface, Rey suggests that there could be a link with the conditions with the dehydration of Eromanga Sea in the Cretaceous and processes that may have occurred on Mars.


Weather services rarely state the absolute humidity because it is not easy to determine. Instead, they state the relative humidity.

  Absolute humidity is the mass of water vapor divided by the mass of dry air in a volume of air at a given temperature. The hotter the air is, the more water it can contain. Absolute humidity is expressed as grams of moisture per cubic meter of air ($\mathsf{g/m^3}$).

  Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity (which depends on the current air temperature). A reading of 100 percent relative humidity means that the air is totally saturated with water vapor and cannot hold any more, creating the possibility of rain.

A better measure of how atmospheric moisture will affect people and the environment is the dew point.

  The dew point is, in short, the point at which dew droplets form on objects like grass – in other words, when a relative humidity of 100 percent is achieved.

  If you want a real judge of just how "dry" or "humid" it will feel outside, look at the dew point instead of the RH. The higher the dew point, the muggier it will feel.

Edit 31 January 2020

Taken from Oppressive, humid conditions for southern Australia as heatwave combines with tropical airmass

  Dew point is the indicator of the amount of moisture in the air ...
  it's the temperature that the air needs to cool to in order to form cloud.

  When temperatures are very high, relative humidity can under represent how much moisture there is in the air, making dew point the better measure.


Does gravity differ from place to place on Earth

There is an entire field of Geophysics called gravimetry dedicated to measuring the magnitude of the gravitational field.

First, we should distinguish between weight (a force) and gravity (an acceleration). Gravity is the acceleration that Earth gives to objects near its surface due to the gravitational force.

The acceleration of an object near the surface of Earth is due to the combined effects of gravity and the centrifugal acceleration from the rotation of Earth. The resulting acceleration is weakest at the equator and maximum at the poles, with a difference in magnitude of about 0.5%, because the outward centrifugal force produced by rotation is larger at the equator than at the poles.

The standard gravity, $ɡ_n$ or $ɡ_0$, (the expected or mid-range value of the gravitational acceleration of an object near the surface of Earth) is 9.80665 $m/s^2$.

Gravimetry measures and studies gravitational anomalies: local variations in topography (e.g., mountains) and geology (rock density) that cause changes in the gravitational field. These gravitational anomalies are measured with instruments called gravimeters. Rocks with lower density, such as sedimentary rocks, result in negative anomalies.

Another effect affecting gravity is altitude, as an increase in altitude will result in a change in gravity of about 0.03% per kilometer. The maximum difference in gravity is about 2 Gal (0.02 $m/s^2$) from sea level to the top of Mount Everest.

The gravity field of Earth has been measured recently with a variety of satellites (GRACE, CHAMP, GOCE). The resulting data can be used to generate global geoids such as EGM96 (geoid calculator). Gravitational anomalies can be extracted by calculating differences with respect to the geoid. The range of variations is of order ±300 $mGal$ (±0.003 $m/s^2$).

Other factors have a small effect on gravity, such as the gravitational force from the Moon and the Sun that causes the tides. The fluctuations associated with these effects are of order 0.2 $mGal$ (2 $µm/s^2$).


Is it true that "All life on earth gets its energy from the sun"? How much biomass is not derived from photosynthesis?

As you say, the existence of organism that live out of chemical compounds expelled by hydrothermal vents (Chemoautotrophs), immediately render the sentence "All life on earth gets its energy from the sun" as an approximation. However, some approximations are pretty good for all practical purposes. Nevertheless, this approximation (even if right), have some deep implications when it comes to assess the likelihood of life in other celestial bodies, like Jupiter's moon Europa, which is the kind of concerns through which I got involved into this topic.

First, there is a very important distinction to make regarding your question,  that is really about

  biomass that does not derive it's energy from the photosynthesis

As you describe it. But that's very different than "subterranean biomass". In particular, the following sentence that you mention:

  ...it is speculated that the subterranean biomass is greater than the
  familiar surface biomass of the earth.

Refers to the biomass within soils (i.e. roots, fungus, bacterias, arthropods, etc.), which is indeed very large. You might include deep ocean ecosystems also. But in all those cases, the energy used by organism was originated by photosynthesis and ultimately by the Sun. The energy get to those sub-surface ecosystem in the form of buried dead organic matter or marine snow. Some works hypothesize about other massive subsurface ecosystems living deep within the oceanic crust, hosting perhaps up to 1/2 to 2/3 of the global biomass. However, as pointed by Whitman et. al. (1998) (the source for the above figure): "current evidence suggests that most of the subsurface biomass is supported by organic matter deposited from the surface". Therefore, it would constitute just one more photosynthetically supported ecosystem.

That been said, the core of your question is "What is the size of biomass that does not derive it's energy from photosynthesis?" And that can be boiled down to: What is the fraction of global net primary production that come from chemosinthesis?.

I don't know of any estimation of that fraction, but to calculate an upper limit for it should be pretty straight forward, at least to have a sense of how good is the approximation of saying that "all life gets its energy from the sun", and how important could be chemosynthesis for the global biomass at most. Let's crunch some numbers:

First consider how much energy is there available for chemosynthesis. To do this it is important to note that no organism can get its energy from the energy gradient within the Earth, so the amount of energy available IS NOT the Earth's internal heat budget. Instead, it correspond to the amount of energy available to life in the form of chemical compounds that come from Earth's interior. According to Gaidos et al., in the most active hydrothermal vent fields, it correspond to 0.157 $MJ/m^2 year$ (read as Mega Joules per square meter per year). The same paper point that

  For comparison, the primary production in the upper ocean is
  equivalent to a biological energy flux of ∼315.36 $MJ/m^2 year$, and this
  is only 0.01% of the total energy available in sunlight.

However, the upper ocean ecosystem is nutrient limited, so the efficiency could be much higher at hydrothermal vents. Perhaps the most efficient ecosystem is the tropical rain forest, with efficiencies in the order of the few percent (~1-3%). So as we are looking for an upper limit, let's say that the ecosystem at the hydrothermal vents have an efficiency of 10%. That leaves us with 0.016 $MJ/m^2 year$ to transform to organic matter.

Now: How much energy is there in a kilogram of organic matter? It varies, but given we are aiming to an upper limit a reasonable (low) typical value is ~10 $MJ/kg$.

We need also to know the surface of hydrothermal vents. To aim again for an upper limit, let's say that all mid-oceanic ridges have the energy availability cited above (referring to the most active hydrothermal vent fields). With 80,000 km of mid-oceanic ridges and about ~15 km wide, we have about 1.2$\times 10^{12}$ $m^2$. Keep in mind that looking at the global distribution of known hydrothermal vents in the figure below, this is most likely a massive overestimation:

Putting all together, our upper limit for the chemosynthetic biomass would be:

$\frac{0.016 MJ/m^2 year \times 1.2 \times 10^{12} m^2}{10 MJ/kg}=1.92 \times 10^9 kg/year$

Now, if we compare that with the 1.7$\times 10^{14} kg/year$ that is produced by photosynthetic primary producers. We get that chemosynthesis produce AT MOST a 0.001% of the biomass.

It can be argued that chemosynthesis happens also outside of hydrothermal vents. But those other locations, like geysers and hot springs, are much smaller. Other more extensive chemosynthetic ecosystems have been proposed, like SLiMEs (Subsurface Lithoautotrophic Microbial Ecosystems), but even if they exist over extensive areas, their productivity would be very small.

To summarize, it would be more correct to say that "More than 99.999% of the life on Earth gets its energy from the Sun". And given all the over estimations we made, I would not be surprised if a more detailed calculation would add a few extra "9's" to that figure.


Is Zealandia really big enough to be called a continent?

In the GSA Today article that Michael linked to in the comments, it says:

  The Glossary of Geology defines a continent as “one of the Earth’s major land masses, including both dry land and continental shelves” (Neuendorf et al., 2005). It is generally agreed that continents have all the following attributes:

  high elevation relative to regions floored by oceanic crust;
  a broad range of siliceous igneous, metamorphic, and sedimentary rocks;
  thicker crust and lower seismic velocity structure than oceanic crustal regions; and
  well-defined limits around a large enough area to be considered a continent rather than a microcontinent or continental fragment.

  The first three points are defining elements of continental crust and are explained in many geoscience textbooks and reviews (e.g., Holmes, 1965; Christensen and Mooney, 1995; Levander et al., 2005; Kearey et al., 2009; Condie, 2015). To our knowledge, the last point—how “major” a piece of continental crust has to be to be called a continent—is almost never discussed, Cogley (1984) being an exception.

and goes on to mention:

  Furthermore, the 4.9 Mkm^2 area of continental crust is large and separate enough to be considered not just as a continental fragment or a microcontinent, but as an actual continent—Zealandia. This is not a sudden discovery but a gradual realization; as recently as 10 years ago we would not have had the accumulated data or confidence in interpretation to write this paper.

This part is important too:

  spatial and tectonic separation, along with intervening oceanic crust, means that the Zealandia continental crust is physically separate from that of Australia. If the Cato Trough did not exist, then the content of this paper would be describing the scientific advance that the Australian continent was 4.9 Mkm2 larger than previously thought.

So to wrap it up, they say:

  Being >1 Mkm^2 in area, and bounded by well-defined geologic and geographic limits, Zealandia is, by our definition, large enough to be termed a continent. At 4.9 Mkm^2, Zealandia is substantially bigger than any features termed microcontinents and continental fragments, ~12× the area of Mauritia and ~6× the area of Madagascar. It is also substantially larger than the area of the largest intraoceanic large igneous province, the Ontong Java Plateau (1.9 Mkm^2).


Halite has a cubic structure as a result of its ionic bonds and ion sizes. This means that the positively charged sodium tends to be surrounded by as many negatively charged chlorine ions as possible (and vice versa) but that attraction is working against the repulsion of positive charges from each other and negative charges from each other. It balances nicely with cubic packing of the atoms.

This does control the cleavage direction but there are other cubic minerals where the ion sizes and charge mean the cleavage is stronger in different directions. A good example is fluorite, calcium fluoride, which often forms cubic-shaped crystals but has octahedral cleavage.


What evidence is backing the claim that the CO₂ we're releasing in the atmosphere is the main cause of climate change?

What evidence is backing the claim that the C02 we're releasing in the
  atmosphere is the main cause of climate change?

As you said in your comment:

  I agree that, if the proof is too complicated to be understood by a
  layman, your only choice is to rely on scientific consensus

Complication regarding proof or evidence based consensus in science is tricky.   Should we accept things that we don't understand, that scientists say are so, like the standard model or should we doubt them.   That's a philosophical can of worms that I'd rather not open, but I can say this, if you can't follow the science, perhaps you shouldn't take a side.  Your time would be better spent learning than doubting.   There is no wisdom in naked skepticism.

That's something many skeptics would be wise to learn.   Skepticism is both great and useless at the same time.   Bart Simpson's a skeptic.   The dumbest kid in the class can say "I'm skeptical about that", and he can answer every question with those 4 words, but he'll never get any smarter.

Applied skepticism is where it's at, and to apply skepticism, you need to understand the argument(s).  Good skepticism requires understanding and, after understanding the argument, then you can intelligently apply skepticism.   Empty doubt is useless.  Good skeptics need to be smart.

This is one argument as to why man made climate science is likely true.   Because there are no good skeptical arguments against it.   Urban heat island - debunked.   Cosmic rays - studied, but no evidence found.   It's the sun?   No, we measure solar output, we'd know.   Mars is getting warmer?  That's incidental.   We're still warming from the last ice age - actually, the opposite is true, we're in a cooling period.  Got any others?   The climate change deniers have figured out that they don't need science to sell their seeds of doubt, they're just selling doubt, but selling doubt isn't a scientific argument.

  What evidence is backing the claim that the C02 is the main cause of
  climate change?

A quick google search will answer this question for you.  Read some of those, and if you still have questions, come back and ask.   This really, really, really has been answered, again and again and again and again.   If you have trouble, I can post some explanations for you.

  CO2 levels have been going up and down for as long as we can look at
  them without human intervention. Eg this NASA graph spanning 400.000
  years

The primary drivers are the milankovich cycle, which leads to the ice-age cycle and feedback mechanisms.  Colder oceans absorb more CO2, warmer oceans release CO2.   CO2 and global temperature have an effect on each other, each driving the other forward or backward depending on how much ice-cover the Earth has.   This is a well understood feedback mechanism that in no way contradicts climate change theory, in fact, they go hand in hand.

  global temperature is still inside the bounds of normal cyclical
  Halocene variations (as seen on wikipedia)

Yes, but the rate of increase is NOT within the bounds of normal Holocene variation.   Also, there is a relation between northern hemisphere summer insolation and temperature.   The direction of the Northern Hemisphere summer insolation is downward right now.  That suggests, without human influence, Earth should be cooling right now, it's not.  It's warming rapidly.

You can say "but the Earth was just as warm 7,000 years ago", and that's about right, but the orbit was different and Earth should have been warmer 7,000 years ago.

  earth temperature has been going up and down for millions of years,
  obviously without human intervention, as seen on the same wikipedia
  page

Hundreds of thousands of years:   Milankovich Cycles

2/5/10/50/100 million years . . . Isthmus of Panama, Himalayas, drifting of Antarctica, Glaciation of Greenland, variation in plant life.

There can be many causes of natural climate change.   One of the ways we know that the current climate change is man made is that we can rule out causes, for example, ocean currents didn't suddenly change in the late 80s.  No new land bridges formed.   Causes are testable and causes have signatures.  CO2 or greenhouse gas driven climate change has a measurable signature.   It's not just that temperature is rising but where it's rising that helps answer these questions, poles vs equator, land vs oceans, upper atmosphere vs lower.

  scientists usually reiterate the first four facts

If you'd read even one scientific study, you'd know this isn't true.  Journalists might mostly reiterate your first four facts, not scientists.

  we know they work because they explain past changes, but this not a
  very strong point since those models have been calibrated using past
  data

There's a principal in science called the double-blind study, where you set up two equal experiments, with one variation and you don't know which experiment has the variation and you study the effects.    This is a good scientific approach but it's not always possible.

You can study the effects of smoking by letting one group smoke and another group not and compare the two groups, but we can't build other Earths to study one with burning fossil fuels and one without - models are all we have.   How accurately the models predict what will happen by 2100 is hard to say, but inaccurate models are better than none.   Take a financial advisory firm that runs models and one that doesn't - and you tell me which one will be right more often.

There's also much more consistency with planet Earth than there is with financial models.  The solar energy the Earth receives year to year varies by less than 0.1%.  Global could cover varies by perhaps 1%-2% year to year.  Snowfall cover varies maybe a little more, volcanic ash comes and goes, but generally leaves the atmosphere pretty quickly, even the largest volcanoes only trigger cooling for a small number of years.   The Earth absorbs heat from sunshine with a small percentage coming from internal heat and volcanoes and it loses heat by radiation.   There are thermodynamic laws that govern heat transfer.    That means the Earth is pretty consistent, having roughly the same orbit around the same star.   By comparison, financial models try to estimate something that's a few orders of magnitude more volatile.

Modeling isn't easy, but it beats blind guessing like the Patriots beating the Jets.   That's true in both studying climate change and in finance.

So, how do we know it's man-made?
Look at the signature.

Earth is warmed by the sun during the day and it radiates energy away at night.   The atmosphere acts like a shield, blocking some of the solar energy from reaching the surface and a blanket catching some of the radiation leaving Earth.

Climate change gases like SO2 and very fine volcanic ash thicken the shield, cooling the Earth - see year without summer.   Climate change gases like CO2 thicken the blanket.   Water is also a greenhouse gas so where CO2 has the biggest effect is low absolute humidity regions like the poles.

Other changes, like albedo, the effect is in visible light, not infra-red.   Ocean current changes are easy to detect because the effects are visible on location.   A stronger mid-atlantic current = warmer European winter.   The climate effects of El Nino, which warms the Earth, are many, but they are well documented.

Heat-trapping greenhouse gas has a signature.   The lower atmosphere warms, the upper atmosphere cools, the tropopause rises and the troposphere loses mass.   The warming can be modeled based on greenhouse gas to be largely polar and the comparing temperature by time of day, the Earth warms most at night, where a hotter sun would do the opposite and warm the Earth during the day and that's where you'd see the larger variation.

Your question implies that scientists ignore all the other possibilities.   Nothing could be further from the Truth.   Scientists (on average) appreciate possibilities and will rarely dismiss valid alternative explanations.   While the theory was first proposed in the 1900s, modern climate change theory had a rebirth in the 1950s, and was the subject of much study through the 60s, 70s and 80s.   It was met, not with immediate acceptance, but decades of skepticism.   It's only now accepted because the evidence in favor is very strong and the evidence for alternate explanations is hovering close to zero.   Decades of research, models that aren't perfect, but fit both matching what's happened so far and going backward, and the signature of the warming matching what is expected from CO2 and the counter theories all failing.    The evidence is very very strong.

All it would take to disprove manmade climate change theory is one unexplained cold year - just one.  One year like the 1970s without a volcano to cause it and the theory is dead.  That hasn't happened.  We've had nothing but warm years for a few decades now.    You could also disprove it by showing a signature that doesn't fit with CO2.  The opportunity (and funding) to disprove climate change is enormous, but you can't disprove a truth, not scientifically.   If it was false, it wouldn't be that hard to show scientific evidence that disproved it.  It's not like this is Rosalind Franklin who worked out how to take photographs of the DNA molecule and she was reluctant to share them with other scientists who'd take the credit for her work.  This is the Earth.  The data, the evidence is out there.  The means to disprove man made climate change - if it was disprovable, are available, and the funding to disprove it is available and significant and they have nothing.   All the evidence still points towards man made climate change theory being right.

(too long?  too preachy?)


Are there any areas on Earth with purplish-colored soil/sand/rock/land?

Soil color is highly dependant on the oxides and other minerals in the composition.  Purplish tones appear to be possible by inclusion of manganese oxide compounds.  There are locations in China that have markedly violet soils.

If you broaden your search to sands as well as soils, there are plenty of examples of garnet-based sands that can appear markedly purple.  California's Pfeiffer Beach is one such location.


Before the Great Oxygenation Event, where was the oxygen?

the great oxygenation event was caused by the evolution of photosynthesis, photosynthesis turns CO2 and water in to sugar and oxygen. so the oxygen came from CO2 and water.

keep in mind CO2 levels were many many times higher (~20X) than today. Hydrogen was not released it was combined with carbon and oxygen to make sugars


What are the mechanisms maintaining the Dune of Pilat?

As per @Richard suggestion, I think the best answer comes from dune-pyla.com. They provide a complete explanation of the evolution of the dune and a couple of great summary figures:

It seems that the material comes in large part from the Banc d'Arguin to the west through aeolian transport. The sand from the bank and adjacent areas is related to the material from the river Garonne to the north.

Part of the reason for the height is that they covered the preexisting Dune de La Grave with a pine forest during the XIX century to stabilize the sand and then the forest was covered by another additional 20-30 meters of sand. The dune is still migrating east at an average rate of around 7-8 m/year and burying the surrounding forest as it migrates.


How to tell if a single day of weather is an anomaly or due to climate change?

I am interested in understanding how to tell if a single day of 'abnormal' weather is due to climate change or not.

You can't. The day-to-day, locale-to-locale variations in weather are huge compared to the changes that occur from year-to-year and decade-to-decade, averaged over the surface of the Earth. Most of those climatological variations are periodic in nature (e.g., El Niño Southern Oscillation, North Atlantic Oscillation; note the "oscillation" in the names). Climate change is the small but steady secular change in climate.

Another way to look at it: Even the most pessimistic of projections is for a 4°C increase over the course of a hundred years. That corresponds to 0.04°C change per year. Weather can bring about a 4°C change over the course of a few minutes. Any one weather event can be attributed to the noisy, flukey nature of weather. Climate change begins to become apparent when one looks at weather events that occur all over the face of the Earth, and over the course of several decades.


What is a Micro-Aethalometer; how do portable Black Carbon (BC) Monitors work?

Following @ Friddy's comment, I started reading Aethlabs AE51 FAQ and was quite surprised!
While a conventional aethalometer use a long tape and move it to the new position after each measurement (which could be as fast as one measurement per minute), the compact device shown in the image in question uses a single filter position, and just keeps measuring as it gets darker and darker as black carbon collects.

Q: Do all the microAeth use the same filters?
A: No. The microAeth AE51 uses a T60 Teflon-coated borosilicate glass fiber filter strip which has 1 sampling location and must be manually replaced. The microAeth MA200 uses a roll of Polytetrafluoroethylene (PTFE) filter material housed in a filter tape cartridge which has 15 sampling locations that can automatically advance. The microAeth MA300 and MA350 use a roll of Polytetrafluoroethylene (PTFE) filter material that is housed in a filter tape cartridge which has 85 sampling locations that can automatically advance. Filter tape cartridges have to be manually replaced much less often than a single use filter strip.

Also:

[...] A guide for measurement limits regarding saturation can be found on the AE51 Specifications Sheet. For example, filters need to be changed according to the following BC concentration/flow rate ranges:

 - Avg.   5 µg BC/m3   for 24 hours    @ 100 ml/min
 - Avg. 100 µg BC/m3   for  3 hours    @ 50 ml/min
 - Avg.   1 mg BC/m3   for 15 minutes  @ 50 ml/min

Compare this to a conventional aethalometer:

Source

Source


What are the dominant elements that oxygen is bonded to on earth?

This answer is basically an expanded version of my comments on this answer here.

If you consider the crust and the mantle, then the most abundant metals are magnesium, silicon, iron, nickel, calcium, aluminium (in that order). Other notable elements would be titanium, chromium, and just about all lithophile elements. The key is to understand that any single oxygen is not exclusively bonded to a single metal. It's bonded to several (different) metals at the same time.

There is an important point to be made here: because we call the minerals "silicates", it's often thought that most of the stuff in there is silicon (and oxygen). In fact, there is actually more magnesium in most of the Earth. Ideal Mg-olivine (forsterite) has double the amount of magnesium than silicon. Enstatite, an orthopyroxene, has the same amount of both elements. It is a common misconception to think of oxygen as being bonded to silicon while the other metals just "hop along". Silica, as SiO2 doesn't actually exist. Not in quartz and not in other silicate minerals. It's not like CO2 that exists as an independent molecule. It's just a convenient, charge-balanced way of representing oxidised silicon that has no existence if there are no oxygens around it. These oxygens are bonded to this silicon cation, but they are also bonded to everything else around it, be it magnesium or iron or whatever. An olivine is not a solid with molecules of SiO2 and MgO, it is an (almost) infinite solid with oxygens bonded to both Si4+ and Mg2+ in a three-dimensional structure. It's just a pile of cations (metals) and anions (oxygen), that happen to conform to combinations of "conventional" oxides because of charge balance.


What mechanism is used to measure ocean currents from cables?

The most likely explanation is that a device similar to a hot wire anemometer has been used; but one that has been designed to be used in oceans.

A hot wire anemometer is basically an electric heater that has been calibrated. The heating element radiates heat into a surrounding medium, depending on the design and  construction of the anemometer, either air or water. The greater the heat loss, the greater the flow of the cooling medium over the anemometer element.

By calibrating the anemometer it is possible to determine the velocity of the medium, in this case ocean current, over the anemometer and from that it is possible to determine the volume flow rate.

Solid state devices, using silicon transistor sensors have also been developed to measure ocean currents.


How does one determine the optimum offset in a seismic survey?

It depends.

Caveat: my experience is with reflection seismic surveys, but I think many of the principles are similar to MASW.

As you guessed: it's an optimization problem. There are lots of factors at play. It's up to the geophysicist to balance the various needs of the survey:

You need to image the target with useful accuracy (small natural bin size).
You want useful signal:noise levels (high fold and trace density).
You want near offsets for good estimates of P-wave reflectivity.
You want far offsets for good estimates of elastic properties (e.g. density).
You may need far offsets to image certain types of geology.
You want the acquisition crew to have enough receivers for the design.
You want to be able to afford the acquisition and processing!

A while ago, I wrote a blog post on the subject: Fold for sale. It's about balancing fold (how many traces go into the stack, basically, a big driver of signal:noise) with cost.

My colleague Evan Bianco and I also did a series on modelling seismic acquisition. If you're into Python at all, there's some code to play with:

The race for useful offsets
Laying out a seismic survey
It goes in the bin
Seismic survey layout: from theory to practice

The greatest minimum offset in a bin is an important consideration, as you guessed. Also notice the spider plots, which try to visualize both maximum offset in a bin, and the range of azimuths going into that bin (which could be important for stress analysis, for example):

It's hard to go into a lot more detail, other than pointing at more things to read. There are a couple of really good books on this subject:

Cordsen et al. (2000), Planning Land 3D Seismic Surveys. SEG Books.
Vermeer & Beasley (2012). 3D Seismic Survey Design. SEG Books.

For a quick overview, I recommend reading this great paper by Norm Cooper:

Cooper, N (2004). A world of reality—designing land 3D programs for signal, noise, and prestack migration: a 2-part tutorial. The Leading Edge 23, October and December, DOI:10.1190/1.1813357 and DOI:10.1190/leedff.23.1230_1.


The width of a unit in a stratigraphic column, or 'log', sometimes represents the average  grainsize of the rock. I can imagine it being keyed to some other property, but grainsize is common. You'll find lots of examples with a quick search for 'sedimentary log'.

The height of a unit typically represents thickness if the vertical axis is length, height or depth. Alternatively, if the vertical axis is time, then the height of a unit corresponds to time duration.

I've tried to illustrate some of the typical layouts here:

On a wireline log, the horizontal axis is some physical property such as natural gamma-ray emission rate or bulk density. Check the legend.

There's no reason not to represent other parameters with the horizontal axis (or the vertical one, or the colour), but then you'd need to be careful about labelling things clearly.

Footnote: often colour is keyed to lithology. This may or may not closely follow the grainsize. Symbols may be added to represent other relevant characteristics of the rock, such as sedimentary structures and fossils.


How much climate history can be reconstructed using marine sediment cores?

The oldest in situ marine sediments recovered by IODP (International Ocean Drilling Program; formerly ODP and DSDP) was (from memory) Late Triassic (so ca. 200 to 230 Ma) and it is as old as in situ marine sediments go, since indeed, as the marine crust gets older, it gets denser and thus is more prone to be subducted. However we do have older marine sediments, that were lifted during various orogenies and that were somewhat metamorphosed but are still viable for paleoclimatic studies (to some reduced extent of course). These lifted and metamorphosed sediments (along with the crust below them and even the upper mantle dragged along) are referred to as ophiolites, and they indeed date as far back as the earliest Phanerozoic (so 500 Ma). As most of the climatic information we are getting from them depends on the planktonic or benthic eukaryotic activity at the time of sedimentation, we cannot really go further back with these.


What does 'reghosted' mean in a seismic cube label?

As you rightly say, data will normally be deghosted during processing.

However, sometimes the deghosting is performed by the acquisition company rather than the processing contractor. The most obvious example would be PGS Geostreamer data, where 'raw' field tapes supplied by PGS to the customer are the upcoming wavefield, with the receiver ghost already removed. This is because the process of combining the velocity sensor and hydrophone data to remove the sea surface reflection is PGS's secret sauce - in many ways building a multi-sensor streamer is the easy part. They work with the true raw data internally, but never supply it to anyone else.

This is normally fine, but if the data is later processed (or reprocessed) by someone else, then complications can arise. If this other processing company wants to perform Full Waveform Inversion, which involves modelling a synthetic wavefield and comparing to the recorded wavefield, then the absence of the receiver ghost will cause an issue. Since the boundary condition at the sea surface has to be reflective to model the multiples correctly. Thus, they may add the receiver ghost back into the data by making an assumption of the sea surface reflectivity and adding it back, creating a 'reghosted' dataset to compare to the synthetics within the FWI.

That said, this would be an internal working dataset for the processing company, not something that would be supplied to the client. So I am surprised you would come across it without knowing what it was, if you see what I mean.


How does one measure what causes earthquakes?

There are a number of causes (this list is probably not complete):

Elastic Rebound of tectonic faults. This is the most common and well known. Here the energy is elastic energy stored as two blocks of rocks move against each other. There is a point where elastic deformation cannot take up the entire movement, and the rock breaks releasing the elastic energy. This is better explained here: Reid's Elastic Rebound Theory (USGS)
Landslides/etc. These typically appear as extremely shallow earthquakes and can often be determined from seismic records.
Cavity collapses. E.g. mines, volcanic systems, caves.
Subterranean explosions / volume expansion. Eg. mining activity, atom bomb tests, volcanic activity (eg. phreatic involving water; or magma injection)
Crystalline phase changes. Fast, deep subduction zones (eg. Tonga) experience very deep earthquakes where the rocks should be too plastic for classic elastic rebound. These are usually interpreted as 'catastrophic' phase changes of olivine -> spinel -> perovskite, and the depths generally match. Eg. Kirby 1991.


Why is there so much more silicon than carbon in the Earth's crust?

So where did it go?

Carbon was never there (or here) to begin with. You need to look at this from the opposite way. By asking "where did it go" you assuming the Earth was here first, with carbon, and then the carbon was removed somehow. But, Earth formed from a gaseous solar nebula that had all the elements.

As the Earth-forming materials started condensing, they consisted primarily of the refractory elements (i.e., elements that form compounds with high melting and boiling points). The volatile elements (i.e., elements that form compounds that you would mostly recognise as gas or liquid).

These volatile elements never accreted to Earth in any significant amounts. They "boiled" away. They were removed by the solar wind farther away. Carbon was mostly in CO, CH4, CO2, etc. These are volatile compounds that never accreted to the Earth, and by the time Earth was large enough to have a gravity to sustain a proper atmosphere, the carbon was all gone.

It's not only carbon. Neon is one of the most abundant elements in the solar system, but there's almost none on Earth. Nitrogen - we only have it in the atmosphere, which is a negligible component of Earth's total mass. Same with hydrogen. Just a small crust of ocean on the surface.

That's why Earth is made of Si, Al, Mg, Fe and Ca oxides. Oxygen bonded to those elements makes very refractory solid minerals.

Further reading

https://en.wikipedia.org/wiki/Frost_line_(astrophysics)

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Earth


How did this stone become encased within different rock?

it was simply an older stone smoothed by water that had fallen into sediment.

This is exactly what happened. There's a name for that: a conglomerate.


Why does El Niño enhance the jet stream?

I'm not sure if it's correct to say that El Niño enhances the jet stream, reading NWS
they seem to state that the affect is more of a shift in the position of the jet stream over the Pacific and North America. I guess any enhancement would be due to a greater temperature contrast between the poles and equator.


Is there a formula that gives the temperature of an object or person exposed to the sun?

It is not an easy problem even for a simple object. The temperature will vary as the conditions change, but the usual approach to such problems is to find the equilibrium temperature for a set of conditions. This is, to find the final temperature that the object will reach if exposed to a given solar irradiation, with air at a given temperature, for given pressure, humidity, wind, etc.

Such equilibrium state will allow you to find the temperature by assuming energy balance. That can be stated  as requiring that the incoming energy into the body equals the outgoing energy, or

$Ẹ_{in} = E_{out}$

To simplify the explanation let's assume the object was in equilibrium with air temperature during the night and we want to calculate its temperature onces the sun is shining on it. In this case the incoming energy will be function of the absorbed solar energy, therefore it will be function of the radiation intensity ($R_{sun}$) that depends on solar elevation, cloud cover, etc. (and can be obtain as a direct output of climate models), the albedo of the object ($\alpha$) and the area exposed to sunlight (i.e. coross-section) ($A$), that will be given by the shape of the object, solar elevation and azimuth. So, that is equivalent to:

$E_{in}=R_{sun} (1-\alpha) A$

Now, the energy leaving the object will have two components.

Radiation: The object will cool down emitting electromagnetic radiation (mostly infrared) according to the Stefan-Boltzmann law.
Conduction: As the object get hotter than the surrounding air, it will loose heat by thermal conduction into it.

So

$E_{out}=\kappa (T - T_{air}) + \varepsilon \sigma T^4 S$

Where $\kappa$ is the thermal conductivity of air, $T$ is the temperature of the object and $S$ its surface area. $\varepsilon$ is the emissivity (that is 1 for a black-body), and $\sigma$ the Stefan-Boltzmann constant.

The three equations above are sufficient to solve for the temperature of the object, but as you can see there are many parameters that depends on the object shape, and material, so it is impossible to generalize.

Also, in the absence of wind, the temperature of the air in contact with the object won't be the same as the surrounding air, further complicating the problem.

Furthermore, in addition to $A$, $\varepsilon$ and $\alpha$ can as well change with solar elevation and azimuth (if the object is made out different materials).

And to further complicate the problem, the thermal conductivity of the air $\kappa$ is a function of temperature, pressure and humidity. And it is not an easy relationship, it is usually tabulated or calculated using empirical formulas.

At engineeringtoolbox.com you can find tables and graphs of $\kappa$ for dry air, here is one example:

But the humidity have also an impact much more difficult to quantify, and whose importance grow with temperature. There is an article at electronics-cooling.com that explain the effect, summarized in the following graph:

So, that is hard enough for an object, let alone for a person. In such case there would a lot more parameters that come to play. Like the amount of insulation provided by clothing, surface and moisture content of the skin exposed to the wind, body heat production, etc.

Apparent temperature

That been said, there are some attempts to estimate the perceived temperature for people including humidity, wind and solar radiation. The best example is perhaps the Wet-bulb globe temperature ($\mathbf{WBGT}$), that consist on the weighted mean of the readings of three different types of thermometers: A normal one, a wet-bulb one (affected by wind and humidity) and a very uncommon black-globe thermometer (affected by solar radiation).

The formula is:

$\mathbf{WBGT} = 0.7 \, T_{wet-bulb} + 0.2 \, T_{black-globe} + 0.1 \, T_{air}$

However, this value is not often used because is very location specific (depend on clouds for example). Nevertheless, perhaps a good approach you can take is to use actual solar irradiation from weather models to compute the temperature that a wet-bulb and a black-globe thermometer would produce, something that I think would be easy to achieve, and then compute the $\mathbf{WBGT}$ with the above formula.

Be aware that the $\mathbf{WBGT}$ value could be useful for people to know how cold/hot it will feel, but won't tell you anything about the actual temperature of different objects exposed to those conditions.


Why are oceanic plates denser than continental plates?

Ocean lithosphere (geophysical definition of crust + upper mantle that acts as a 'plate') is primarily of basaltic composition - the upper levels are basalt and the lower levels are gabbro. The top levels have been proven with boreholes, whilst the lower levels have been inferred from transform fault sampling and comparisons with ophiolites. This sequence is produced by partial melting of mantle peridotite at a fairly controlled rate. So much so that basalts formed in this way even have a specific composition "MORB" (Mid Ocean Ridge Basalt).

In contrast, continent lithosphere is more complex and tends to be of a 'granitic' composition. This includes granites but can also include a lot of metamorphic rocks (eg. gneiss) and sediments. Sediments are lower density anyway (high pore space), but so are quartz-rich rocks such as granites. The various processes that build continents tend to favour silica rich compositions, resulting in this bulk "granitic" composition. For example, limited partial melting will initially produce high silica, high alkali melts. Erosion will tend to break down most common minerals before quartz - leaving quartz-rich sediments (hence sandstone is primarily quartz). Metamorphism of pelites (rocks rich in Al and Si) will tend from the initial mudstones & basalts through to gneisses & migmatites (which have a lot of quartz and feldspar). Migmatites are partially melted - and the melted bits are essentially granite.

Basalt is denser than granite. On gravity surveys, basalts and gabbros will appear as positive anomalies, whilst granites and sedimentary basins will appear as negative anomalies.


Fossil groundwater is water that has been trapped below the surface for several thousands of years. It is considered non-renewable as natural recharge on human timescales is practically zero. This is because the permeability/transmissivity of the overlying strata is very low.

However, on geological timescales the aquifer will recharge as pumping the water out of the aquifer decreases the hydraulic head, and therefore increases the gradient over the aquitards sealing the aquifer. Therefore the recharge of the aquifer actually speeds up by withdrawing water, although probably not in amounts humans can profit from.

Since you're asking about techniques to recharge, techniques similar to those used for shallower aquifers could be applied. In the Netherlands regeneration of groundwater is performed to decrease the stationary drawdown of the groundwater by the pumping which leads to damages for farmers. This is often performed by pumping surface water into the aquifer at some distance so the aquifer is recharges artificially and the groundwater table rises.

On the other hand, recharge of these fossil water aquifers in arid areas such as the subtropics is probably infeasible, even though it would be technically possible.


Why is "at least a small tilt" between rotation and magnetic axis required by models of magnetic field formation?

"Tilt" is a consequence of a convecting metal inner core....not a "necessity". In the earth's case, that tilt has, over time, wandered from 0 to 180 degrees, sometimes with some temporal regularity, other times completely randomly. The science writer likely poorly paraphrased Professor Ingersoll's curiosity regarding the existence of a molten metal core deep within Saturn.


How is it possible that only the bottom half of the moon was showing?

It depends on the season and even more on latitude.

At any given time, the same side of the Moon faces the Sun.  Where you stand on Earth doesn't change which part of the Moon is lit, but if you think about the orientation of people on the earth, people in the Northern and Southern Hemisphere are "upside down" to each other and people on the equator are perpendicular.   The Moon doesn't change but the point of view of people on Earth relative to the Earth's surface makes a full 360 degrees of rotation based on latitude, so the same moon at the same time can appear as a left crescent, a right cresent, a boat and a yamaka depending on the person's latitude at the time of viewing.

Also explained here.

And this should probably be astronomy.


Does the relative abundance of radioactive isotopes reflect their half-lives?

Yes, the general idea you have is correct: isotopes with relatively short half-lives are found in quantities so minute as to be marginally detectable, and then only if they are being produced by something else: either as decay products of some long-lived isotope, or by cosmic-ray bombardment.
An example is gadolinium-150. This has a half-life of about 1.8 million years, and I believe simply does not occur naturally at all.  Gadolinium-152, with a half-life of about $10^{14}$ years, does occur naturally.
So whatever primordial gadolinium-150 there was has gone (in 4 billion years, you get a decrease of a factor of about $10^{669}$: the Earth contains around $10^{50}$ atoms, so there is a chance of $1/10^{619}$ of finding an atom of it on Earth).  Unfortunately in order to know how much there was you would need to understand nucleosynthesis in supernovae in considerable detail (gadolinium is heavier than iron and so originated mostly or entirely in supernovae), and I don't.  But I think it's safe to say that they probably made at least some, on the grounds that anything we do in the way of crashing particles into things to make isotopes (which we have done to make $^{150}\mathrm{Gd}$) supernovae also do, except much, much more.  If we assume the Earth was only a million years old, then about $68\%$ of the primordial $^{150}\mathrm{Gd}$ would still be here: we'd find it.
Now of course, there are two catches here:

perhaps the $^{150}\mathrm{Gd}$ has all gone somewhere secret where we can't find it;
this all rests on the idea of supernova nucleosynthesis.

So to answer the first: if this was true it would be utterly extraordinary.  In particular we spend a lot of time (really a lot of time) trying to isolate different isotopes of elements: people go to really enormous efforts to distinguish between different isotopes of uranium for instance.  This is something you can't do chemically, because the different isotopes have the same chemical properties.  Instead you have to do things like spin them in very high-speed centrifuges, or use mass spectrometers.  These things just don't exist naturally on Earth, so, since we do find other isotopes of gadolinium (including ${}{150}\mathrm{Gd}$, which is not stable), how come we don't find this one?  Well, we don't find it because it's not there, of course.
The second problem is perhaps more severe: people who believe the Earth is a million years old probably have no truck with supernovae at all, or are happy to just argue that, well, supernovae don't produce some isotopes because they just don't.  I don't think there's a useful argument against that.


How to Calculate the Equilibrum Function for use in Tide Calculations using Harmonic Constituents

The equilibrium tide is a theoretical concept developed by Newton in the 17th century that considers only the gravitational pull by the Moon and the Sun and the centrifugal forces, with no inertia, no friction and no land masses. From the NOAA definitions:

  equilibrium theory — A model under which it is assumed that the waters covering the face of the Earth instantly respond to the tide-producing forces of the Moon and Sun to form a surface of equilibrium under the action of these forces. The model disregards friction, inertia, and the irregular distribution of the land masses of the Earth. The theoretical tide formed under these conditions is known as the equilibrium tide.

Lets consider as a first cut the two tide producing forces associated with just the Moon and Earth systems. The two are the centrifugal force of Earth from the center of mass of the Moon-Earth system and the gravitational attraction due to the Moon. For the point closest to the Moon:

$$ Force = \frac {GM_1M_2}{(R-r)^2}  - \frac{GM_1M_2}{R^2} $$ where R is the distance between Earth and Moon and r is Earth's radius. It gets a bit more complex for other points on the surface because instead of R you have to use $$R\pm r cos(lat) $$ for the gravitational force.

Ultimately, it comes down to a set of horizontal forces that tend to concentrate water in two theoretical points: one, the closest to the Moon and two, the farthest from the Moon. An equilibrium state would be reached, called equilibrium tide, that results in an ellipsoid with its two bulges directed toward and away from the Moon.

In practice, this equilibrium ellipsoid does not develop because of the rotation of Earth, the Coriolis acceleration and the fact that the tidal wave feels the ocean bottom and it is subject to friction. Going beyond the equilibrium theory of the tide, the dynamic theory of tides (developed by Euler, Laplace and Bernoulli) includes all these concepts (friction, inertia, Coriolis, land masses,...) and provides a better approximation to the observed tides.

My recommendation to understand tidal constituents is to use some decent tidal harmonic analysis package like t_tide for Matlab, which is likely to be the tool that NOAA is using to generate their harmonic constituents in the first place. If you really want to get into the details, then the best option is to go to the still likely best source available. That will the 1973 book "The Analysis of Tides" by G. Godin.

Pawlowicz, R., B. Beardsley, and S. Lentz, "Classical Tidal Harmonic Analysis Including Error Estimates in MATLAB using t_tide", Computers and Geosciences, 28, 929-937 (2002).

Godin, G. (1973). The analysis of tides., by Godin, G.. Liverpool (UK): Liverpool University Press, 264 p.


How to search for the nearest non nan value in 2d xarray dataset

If I were you, I would exclude the NaN values and then perform gridding on the resulting irregularly spaced data.

There are already the tools to perform this in Python and using the library SciPy

https://scipy-cookbook.readthedocs.io/items/Matplotlib_Gridding_irregularly_spaced_data.html

But please document exactly what step you are doing and why. Excluding data is always ... interpreting the data.


When the Earth was newly formed by collisions with asteroids, comets, planetesimals and other debris of the early solar system 4.6 billion years ago, the planet was incandescent and the mantle hotter and more fluid than it is today. Just as you have heard, the heavy metals sank toward the centre.

And just as you say, there is a tiny place at the very centre where almost all the mass of the Earth and therefore almost all the gravity is outside this central point. Imagine this central point to be a cannonball. There is no enormous mass at its centre, pulling it down, and the gravitational field of the mass above it is pulling it outward and upward, so why doesn't it migrate back toward the surface?

You need to remember that only the imaginary cannonball is in this exclusive central position. For any substance close to it but not at the absolute centre, there will be more mass to one side of it than the other, so there will be a gravitational force pulling it toward that direction, in other words, toward the centre of mass.

The other thing to remember is that on top of the imaginary cannonball, in all directions, is a column of molten material reaching nearly 4,000 miles right up to the surface, and this column has enormous weight and pressure. Because of this pressure there is a substantial region where the iron-nickel core is solid. How did infalling heavy metals reach the centre if there is a solid mass there? Well,it wasn't always solid, and there was a stage when it was liquid. The gravity-free zone at the Earth's centre is purely theoretical and doesn't allow the centre to behave as though it were in zero gravity.