Geologists study fossil rat urine
By Sid Perkins
UPI Science News
WASHINGTON, July 24 (UPI) -- The accuracy of a standard technique of
dating artifacts could be called into question by new evidence from an old
source -- ancient packrat urine.
Researchers report today in the journal Science that the amount of
radioactive chlorine in crystallized urine from packrat dens in Nevada
does not match the amount expected from carbon-14 data.
The team, led by scientists at the New Mexico Institute of Mining and
Technology in Socorro, analyzed 40 urine samples from four sites.
Researchers found the samples to be up to 38,000 years old.
Half of the radioactive carbon-14 in a sample decays every 5,730 years, so
measuring the amount of carbon-14 in an object will tell its age. The same
measurements can be performed with radioactive chlorine, which has a
half-life of about 320,000 years.
Researchers compared the amount of carbon-14 in leaves and twigs from the
packrat dens to the amount of radioactive chlorine in the crystallized
urine binding the material together. They found variations in amounts of
radioactive carbon and chlorine did not match during a period between
20,000 and 10,000 years ago.
The scientists believe that a 40 percent increase of carbon dioxide in
the atmosphere during that period may be related to the mismatch. If a
significant amount of that increased carbon dioxide had been dissolved in
the ocean for a long time, they say, the amount of carbon-14 in the
atmosphere may have been diluted. This, in turn, would affect the accuracy
of carbon dating objects from that period.
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