[meteorite-list] Fw: term definitions and usage

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Sun, 24 Jul 2011 21:54:18 -0400
Message-ID: <8CE1884E68B7CEB-C04-99C6_at_webmail-m083.sysops.aol.com>

Chris wrote:
"Ga is billions (gigayear) of years"

... and one reason it is in the scientific lit is because it is much
less confusing on the eye though nothing in rocks is a US trillion
years old (twelve zeros);

Many Europeans consider the billion with 12 zeros (1,000,000,000,000),
while in the US and many other countries, it has been considered nine
zeros, a thousand million. Giga has the benefit of only referring to
nine zeros everywhere ...

Here's the rest of the prefixes fyi:
http://en.wikipedia.org/wiki/Gigaannum#SI_prefix_multipliers

SI prefix multipliers

  ka (for kiloannum), is a unit of time equal to one thousand (10^3)
years.
  Ma (for megaannum), is a unit of time equal to one million (10^6)
years. It 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 65 Ma (65 million years)
ago (ago may not always be mentioned; if the quantity is specified
while not explicitly discussing a duration, one can assume that "ago"
is implied; the alternative but deprecated "mya" unit includes "ago"
explicitly.). 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 gigaannum), is a unit of time equal to 10^9 years (one billion
on the short scale, one milliard on the long scale). It 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 4.57 Ga (4.57 billion years) ago.
  Ta (for teraannum), is a unit of time equal to 10^12 years (one
trillion on the short scale, one billion on the long scale). It 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 star.
  Pa (for petaannum), is a unit of time equal to 10^15 years (one
quadrillion on the short scale, one billiard on the long scale). 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), is a unit of time equal to 10^18 years (one
quintillion on the short scale, one trillion on the long scale). The
half-life of tungsten-180 is 1.8 Ea.[20]


Best wishes
Doug




-----Original Message-----
From: Chris Peterson <clp at alumni.caltech.edu>
To: meteorite-list at meteoritecentral.com
Sent: Sun, Jul 24, 2011 9:37 pm
Subject: Re: [meteorite-list] Fw: term definitions and usage


Ga is billions (gigayear) of years. Ma is millions (megayear) of years.
"a" is the most commonly used symbol for year (from annus) in
scientific publications.?
?
Chris?
?
*******************************?
Chris L Peterson?
Cloudbait Observatory?
http://www.cloudbait.com?
?
On 7/24/2011 7:26 PM, Richard Montgomery wrote:?
>?
> Hello List,?
>?
> Another neophyte question (I can use some clarification): when / how
are?
> the time-measurements (relatively speaking) designations "Ga" and Ma"?
> used, and their respective differences??
>?
> (I believe I know the difference through context, but why go through
so?
> many papers and texts with the question-mark over my head?)?
>?
> Sincerely,?
> Richard Montgomery?
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Received on Sun 24 Jul 2011 09:54:18 PM PDT