Re: Dating of 1470
J. Moore (j#d#.moore@canrem.com)
Sat, 22 Jul 95 12:18:00 -0500
This post was written a week ago but was eaten by my Internet
server (reportedly it was delicious); I thought it offers useful
additional info on the question:
Ha> I understand that KNM-ER 1470 was originally dated at 2.9 million years
Ha> by Richard Leakey due to separate analyses that agreed (Fitch & Miller,
Ha> Maglio)
Ha> Why were these analyses rejected? What led to the consensus for the
Ha> present dating of 1.8 million years?
The dating of KNM-ER 1470 was caught up in the dating problems of
the KBS Tuff (a layer of volcanic residue, this one named after Kay
Behrensmeyer) and the Tulu Bor Tuff beneath it. The first dating
attempts of the KBS Tuff by means of a potassium-argon resulted in
a scatter of dates; obviously not a good sign. Later attempts were
made with 40Ar/39Ar step heating and these gave the quite early dates
which seemed good to Leakey (a family thing there; Leakey is
pretty good on the subject with the exception of expecting, like his
folks, to find a very early *Homo*). They did seem out of step to
most others, however, and, more critically, they didn't match up
with the faunal evidence.
The suid (pig) fossils around Africa appear with such frequency
that they're are a good test of dating accuracy. If your dates
don't match up with the pigs you would expect to see at that date,
it's generally considered you should double-check your dates. The
pigs found in the Tulu Bor Tuff (which was tentatively dated at
about 3.18 mya) were of the sort seen at Omo in Shungura Member G
and Bed I, and this last was firmly dated at 1.8-1.7 mya (Omo is
well-dated).
Later studies used different techniques to separate out datable
pumice and gave dates for the KBS Tuff of 1.82 mya (plus or minus
0.4 mya -- remember there is always a plus or minus altho this is
often not stressed). More recent tests have confirmed these
dates, giving K/Ar (potassium-argon) dates of 1.8 mya (plus or
minus 0.1 mya) by Drake et al. and 1.89 mya (plus or minus 0.1
mya) by McDougal et al., both in 1980.
This info was from Tanner, 1981 *On Becoming Human*, pp. 243-247.
Jim Moore (j#d#.moore@canrem.com)
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