Sterling K. Webb wrote:
Here is the problem with my attempting to deal
with the data (the isotopic anomalies). People seem
to consider me instead a supporter of various theories,
whacky or not, Firestone's or any other's, about
extinctions. I have no brief for these theories.
I am interested only in what exterior astronomical
events created these isotopic anomalies. They
require an explanation.
Hi Sterling,
Just for clarity: I for one have been well aware that you were not a supporter
of wacky theories, but just interested in these new suggestions, with an open as
well as critical mind. I also agree with you that there are a few things in
Firestone's isotopic data that are interesting and merit consideration of what
might be the cause.
More comments below:
Marco mentions the vagaries of radiocarbon
dating and so forth. It's obvious nobody is
reading the reference I gave for Firestone's
earlier paper on them:
<http://www.centerfirstamericans.com/mt.html?a=36>
It derives, among other things, from
trying to calibrate those vagaries.
I did read the reference (with much interest!), but the calibration attempts of
Firestone (and others before him, e.g. Stuiver and Pearson) do not remove the
vagaries and will never do. These vagaries are the result of the fact that for >
30,000 years ago, 14C levels due to decay of the isotope are just that low that
they will be *never* reliable to measure. You can try to calibrate for wiggles
in atmospheric C14 content over time such as has been done for younger periods,
but that is not the true issue for ages in this range: the true issue is that
the method istelf starts to fail. 14C is not suited to dates of several Ka. The
problem is, that there are little alternative dating methods for age ranges in
the range of a few Ka, other than thermoluminiscence (which require suitable
sediments or heated crystaline rock). Basically, it is too old for 14C, too
young for K/Ar or Ar/Ar, while fission track isn't realy suited for this time
period too. There is a whole bunch of other isotopic methods, but these all have
their issues. Hence this is why 14C dates are attempted, but they should always
be taken with much caution. Sometimes, people forget that: "the laboratory says
it is that old, so it is true".
Dating problems and chronology is a specialty of me, part of my PhD dissertation
revolved around that issue, although my focus is more on the earlier Palaeolithic.
I have dealt with geochronologist as part of my research. Some (not all), even
pretty good ones, do not seem to get that field conditions of sample environment
as well as geological conditions in the past are not laboratory conditions, and
the true error on a date is not just determined by the standard deviation on a
machine reading.
Below a strata well-known to date geologically
to 10,000 BP (before present) are artifacts with
thermoluminescent dates of 12,400 BP but with
radiocarbon dates that are almost recent, 2880 BP.
There are a number of these sites, including
one where there is an area with an archaic
cultural items whose radiocarbon date is 160
years old!
...and this happens often in the reality of archaeological fieldwork. I would
think of a contamination issue here first, as 14C is susceptible to this, or
taphonomic issues of reworking and sedimentation environment, stratigraphic
disconformities etc. E.g., could it be a lag deposit incorporating material from
a large timespan? Could organic materials be reworked into the deposit by
bioturbation? Could organic material be washed in by groundwater action, soil
formation? This is exactly where laboratory guys often go blind on their dates
and laboratory technical accuracy, while not properly taking into account the
context and taphonomic history of the samples. You might be surprised, but that
happens a lot, even in prestigeous papers published in top journals. The
solution to this kind of dating problems does usualy not come from employing a
"better" technique or increasing ist "accuracy", but from thorough taphonomic
studies.
(another thing here is to consider whether the "archaic" material realy is
"archaic", but that might be my bias as an archaeologist working with a.o. Lower
palaeolithic materials. We have come to realise there, that typology not always
works, especially with materials that appear to be "crude").
- Marco
-----
Dr Marco Langbroek - Pleistocene Archaeologist
e-mail: [EMAIL PROTECTED]
website: http://home.wanadoo.nl/marco.langbroek
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