as a millennium in anthropology and calendar uses. The prefix multiplier "ka" is typically used in geology, paleontology, and archaeology for the Holocene and Pleistocene periods, where a non−radiocarbon dating technique such as ice core dating, dendrochronology, uranium-thorium dating or varve analysis is used as the primary method for age determination. If age is determined primarily by radiocarbon dating, then the age should be expressed in either radiocarbon or calendar (calibrated) years Before Present. Ma (for megaannus) – a unit of time equal to one million or 106 years. The suffix "Ma" is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics. In astronomical applications, the year used is the Julian year of precisely 365.25 days. In geology and paleontology, the year is not so precise and varies depending on the author. Ga (for gigaannus) – a unit of time equal to one billion or 109 years. "Ga" is commonly used in scientific disciplines such as cosmology and geology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.54 Ga (4.54 billion years) ago and the age of the universe is approximately 13.8 Ga. Ta (for teraannus) – a unit of time equal to one trillion or 1012 years. "Ta" is an extremely long unit of time, about 70 times as long as the age of the universe. It is the same order of magnitude as the expected life span of a small red dwarf. Pa (for petaannus) – a unit of time equal to one quadrillion or 1015 years. The half-life of the nuclide cadmium-113 is about 8 Pa. This symbol coincides with that for the pascal without a multiplier prefix, though both are infrequently used and context will normally be sufficient to distinguish time from pressure values. Ea (for exaannus) – a unit of time equal to one quintillion or 1018 years. The half-life of tungsten-180 is 1.8 Ea. Abbreviations for "years ago" In geology and paleontology, a distinction sometimes is made between abbreviation "yr" for years and "ya" for years ago, combined with prefixes for thousand, million, or billion. In archaeology, dealing with more recent periods, normally expressed dates, e.g. "10,000 BC", may be used as a more traditional form than Before Present ("BP"). These abbreviations include: Use of "mya" and "bya" is deprecated in modern geophysics, the recommended usage being "Ma" and "Ga" for