INTCAL98 defines the C14 calibration back 26,000 years. There have been
subsequent calibrations using deposits in caves that push things back to
about 45,000 years, with somewhat less accuracy, and these aren't normally
used in standard C14 dating. What curve are you looking at that goes back
50,000 years?
But it doesn't really matter. The problem is there is no way to connect
changes in C14 levels with any kind of impact events. Barringer is not very
accurately dated, and there was enough other stuff going on around the
Younger Dryas to cause changes without invoking an impact. Note that I'm not
saying here whether one or more impacts did or didn't occur over the C14
data record, only that there is no solid, datable evidence that can be
matched to that record. Given all the possible things that can affect C14
production (and especially C14 uptake), it is almost impossible to use the
record to demonstrate anything.
IMO Barringer is a horrible example in any case, if you believe that
neutrons are produced. For such a small impact to actually produce enough
neutrons to significantly affect the worldwide C14 levels would also result
in very obvious radioisotope anomalies in the surviving iron meteorite
samples, give iron's high neutron absorption cross section. You'd be better
off trying to sell this theory with a collision with a comet or other stony
body than an iron.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "E.P. Grondine" <epgrond...@yahoo.com>
To: <meteorite-list@meteoritecentral.com>
Sent: Thursday, October 29, 2009 8:44 PM
Subject: [meteorite-list] Neutron production in hypervelocity impacts -
wasOdessa date
Hi Chris-
"The C14 calibration data only goes back 24,000 years,"
Try 50,000 years - INCAL98.
"and there have been no confirmed significant impacts during that time,"
Barringer?
"and not even any well dated minor impacts. So how can spikes in the
calibration curve be linked to impacts?"
Actually, take a look at the INTCAL98 chart running back 50,000 YEARS.
Note the spike and then the bump at 10,900 BCE. This is what is started
driving Firestone - he saw a supernova at first, then a supernova
injecting comets.
"Even given a large impact (a big given)"
Take a look at Barringer, and look at what has been found at Sheriden
Cave, and by the way note the First Peoples' accounts of these multiple
large comet fragment impacts at:
http://forum.palanth.com/index.php/topic,1093.0.html
I suppose the denial will go on for years, even after the AGU
discussion/debates coming up soon.
"there are plausible explanations for how this would affect C14
concentrations; far more plausible than the very unlikely production of
neutrons."
Yes, I know the releases energies are very high, and yes, there are
multiple explanations, - sun, magnetosphere, supernova, etc. It will fall
to those with more intelligence than I myself have left to sort it all out
But plese note that the one spike that got to me was the spike roughly at
the time of the Barringer Crater impact. Firestone is proposing multiple
supenovas, from what is being sent around, but it sure looks to me like
the energies in large hypervelocity impacts are indeed freeing neutrons.
In the meantime, OSL dating for Odessa will be an open question for me.
E.P. Grondine
Man and Impact in the Americas
(a pretty good book despite its flaws - write me off list for the
meteorite list special.)
PS - I have been wrong in the past, and reserve the right to be wrong both
now and in the future.
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