[meteorite-list] Fw: term definitions and usage

[MexicoDoug]

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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