[meteorite-list] Odessa

From: Matson, Robert D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Wed, 28 Oct 2009 12:10:52 -0700
Message-ID: <7C640E28081AEE4B952F008D1E913F1701F8C0B6_at_0461-its-exmb04.us.saic.com>

E.P. wrote:

> Take a look at the INTCAL98 14C calibration chart. Major spikes appear
> to map to impacts.

"Spikes" in the C14 calibration chart can be caused by a number of
factors
(including measurement uncertainty/error). But the main cause of
variability
in the production rate of atmospheric C14 is simply variation in the
flux
of cosmic rays. Cosmic ray intensity is modulated by both the strength
of
the earth's magnetosphere and the sun's solar wind, neither of which is
constant.

>From the other side of the equation, atmospheric C12 is ALSO modulated
by earthly processes (e.g. volcanic eruptions, ocean temperature
changes)
which can produce regional anomalies in the samples used to build the
radiocarbon calibration curves.

There is no evidence that large impacts can cause nuclear reactions that
release neutrons. There isn't sufficient energy or fissionable material,
so I have difficulty coming up with a mechanism which could cause a
large spike in neutrons. I suppose if an impactor had an anomolously
high
beryllium content and it happened to hit an earth location with rich
uranium deposits, then you could get a small neutron hiccup. But
siderites
are very low in berrylium (< 10 parts per billion), so that's a no-go on
Odessa. Even chondrites typically have only a few hundred parts per
billion.

--Rob
Received on Wed 28 Oct 2009 03:10:52 PM PDT