by neufer » Sat Nov 16, 2019 8:34 pm
Chris Peterson wrote: ↑Sat Nov 16, 2019 2:43 pm
bls0326 wrote: ↑Sat Nov 16, 2019 2:34 pm
The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions?
I have not seen that before and Google search does not show any such symbol.
"G" is the standard SI prefix for billion (i.e. 10
9). It represents "giga".
Properly applied to years, it should be "Ga", as "a" is the SI symbol for year.
But both "y" and "yr" are pretty commonly used.
https://en.wikipedia.org/wiki/Year#SI_prefix_multipliers wrote:
<<
For the following, there are alternative forms which
elide the consecutive vowels, such as kilannus, megannus, etc.
ka (for kiloannum) – a unit of time equal to one thousand, or 103, years, or 1 E3 yr, also known 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: e.g. ice core dating, dendrochronology, uranium-thorium dating, or varve analysis; is used as the primary dating 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 megaannum) – a unit of time equal to one million, or 106, years, or 1 E6 yr. The suffix "Ma" is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics to signify very long time periods into the past or future. For example, the dinosaur species Tyrannosaurus rex was abundant approximately 66 Ma ago. The duration term "ago" may not always be indicated: if the quantity of a duration is specified while not explicitly mentioning a duration term, one can assume that "ago" is implied; the alternative unit "mya" does include "ago" explicitly. It also written as "million years" (ago) in works for general public use. In astronomical applications, the year used is the Julian year of precisely 365.25 days.
Ga (for gigaannum) – a unit of time equal to 109 years, or one billion 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 ago.
Ta (for teraannum) – a unit of time equal to 1012 years, or one trillion 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 petaannum) – a unit of time equal to 1015 years, or one quadrillion 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 exaannum) – a unit of time equal to 1018 years, or one quintillion years. The half-life of tungsten-180 is 1.8 Ea.
...............................................................
In astronomy, geology, and paleontology, the abbreviation yr for years and ya for years ago are sometimes used, combined with prefixes for thousand, million, or billion. They are not SI units, using y to abbreviate the English "year", but following ambiguous international recommendations, use either the standard English first letters as prefixes (t, m, and b) or metric prefixes (k, M, and G) or variations on metric prefixes (k, m, g). In archaeology, dealing with more recent periods, normally expressed dates, e.g. "22,000 years ago" may be used as a more accessible equivalent of a Before Present ("BP") date.Use of mya and bya is deprecated in modern geophysics, the recommended usage being Ma and Ga for dates Before Present, but "m.y." for the duration of epochs. This ad hoc distinction between "absolute" time and time intervals is somewhat controversial amongst members of the GSA: Geological Society of America.>>
[quote="Chris Peterson" post_id=297068 time=1573915434 user_id=117706]
[quote=bls0326 post_id=297067 time=1573914861 user_id=140793]
The merger simulation video shows time as Gyrs, running from 0 to 3.9 or so. Is G a symbol for billions?
I have not seen that before and Google search does not show any such symbol.[/quote]
"G" is the standard SI prefix for billion (i.e. 10[sup]9[/sup]). It represents "giga".
Properly applied to years, it should be "Ga", as "a" is the SI symbol for year.
But both "y" and "yr" are pretty commonly used.[/quote][quote=https://en.wikipedia.org/wiki/Year#SI_prefix_multipliers]
[float=right][img3="Ma (Marjorie Main) and Pa (Percy Kilbride) Kettle"]https://upload.wikimedia.org/wikipedia/en/6/67/MaandPaKettle.jpg[/img3][/float]
<<[b][color=#FF00FF]For the following, there are alternative forms which
elide the consecutive vowels, such as kilannus, megannus, etc.[/color]
[b]ka (for kiloannum) – a unit of time equal to one thousand, or 10[sup]3[/sup], years, or 1 E3 yr, also known 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: e.g. ice core dating, dendrochronology, uranium-thorium dating, or varve analysis; is used as the primary dating 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.
[color=#FF0000]Ma (for megaannum) – a unit of time equal to one million, or 10[sup]6[/sup], years, or 1 E6 yr. The suffix "Ma" is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics to signify very long time periods into the past or future. For example, the dinosaur species Tyrannosaurus rex was abundant approximately 66 Ma ago. The duration term "ago" may not always be indicated: if the quantity of a duration is specified while not explicitly mentioning a duration term, one can assume that "ago" is implied; the alternative unit "mya" does include "ago" explicitly. It also written as "million years" (ago) in works for general public use. In astronomical applications, the year used is the Julian year of precisely 365.25 days.[/color]
Ga (for gigaannum) – a unit of time equal to 10[sup]9[/sup] years, or one billion 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 ago.
Ta (for teraannum) – a unit of time equal to 10[sup]12[/sup] years, or one trillion 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.
[color=#0000FF]Pa (for petaannum) – a unit of time equal to 10[sup]15[/sup] years, or one quadrillion 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.[/color]
Ea (for exaannum) – a unit of time equal to 10[sup]18[/sup] years, or one quintillion years. The half-life of tungsten-180 is 1.8 Ea.
...............................................................
[color=#0000FF]In astronomy, geology, and paleontology, the abbreviation yr for years and ya for years ago are sometimes used, combined with prefixes for thousand, million, or billion. They are not SI units, using y to abbreviate the English "year", but following ambiguous international recommendations, use either the standard English first letters as prefixes (t, m, and b) or metric prefixes (k, M, and G) or variations on metric prefixes (k, m, g). In archaeology, dealing with more recent periods, normally expressed dates, e.g. "22,000 years ago" may be used as a more accessible equivalent of a Before Present ("BP") date.Use of mya and bya is deprecated in modern geophysics, the recommended usage being Ma and Ga for dates Before Present, but "m.y." for the duration of epochs. This ad hoc distinction between "absolute" time and time intervals is somewhat controversial amongst members of the GSA: Geological Society of America.[/color][/b]>>[/quote]