🚀 go-pugleaf

In article <1992Apr09.141649.37267@watson.ibm.com>, platt@watson.ibm.com (Daniel E. Platt)
   writes:
|> In article <1992Apr8.193655.27457@cs.yale.edu>, rescorla@rtnmr.chem.yale.edu (Eric Rescorla) writes:
|> |> In article <1992Apr08.173630.1785@watson.ibm.com> platt@watson.ibm.com (Daniel E. Platt) writes:
|> |> >In article <1992Apr8.161532.24698@cs.yale.edu>, rescorla@rtnmr.chem.yale.edu (Eric Rescorla) writes:
|> |> >The concentrations have not been ~ constant over time.
|> |> >
|> |> >See some of Colin Renfrew's work...  You'd find it interesting...
|> |> It was my impression that they had been constant to within say 50%,
|> |> which was all I meant to suggest.
|> 
|> 50%?  Wow!  That's essentially 1 half-life... or around 8,000 years...
|> 

The pre-bomb variations in atmospheric C-14 concentration over the last ca. 8000 years were 
much less than 50%.  The maximum deviation from pre-bomb "modern" values 
(say, the value for the year 1950) occurs toward the end of the dendrochronological record 
(i.e. at 7000-8000 y.b.p.).  At that time, the atmospheric C-14/C-12 ratio was about 10% higher 
than the 1950's pre-bomb value.  This corresponds to an error of about -750 years -- that is, 
an "uncorrected" C-14 age obtained by assuming a constant atmospheric C-14 concentration is 
about 750 years too young.

A good review of atmospheric C-14 variations is Damon, PE, Lerman, JC, and Long, A, 1978, 
Temporal Fluctuations of Atmospheric C-14: Causal Factors and Implications.  Annual Rev. of 
Earth and Planetary Sci., v6, pp457-94.

-- 
Henry Shaw, Earth Sciences Dept., LLNL |    All opinions are my own.
Internet: shaw4@llnl.gov               |  
CIS: 76347,2523                        |
Fidonet: Henry Shaw at 1:161/55        |