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Re: Radiocarbon Dating



    Radio-Carbon dating CAN be used for dates up to ~80,000 years ago.
However, the error range increases drastically once you pass 50,000 years.
Also, it is of little use in anything more recent than 5,000 years ago.
(The item being tested must be organic based, and must be dead - tests on
live mollusks showed an age of 2000 years).

    If a fossil is completely replaced (permineralized), then it would be
useless in a similar test - because it no longer is organic.  Fortunately,
we are able to date older fossils using the radiometric breakdown of other
elements (Potassium-Argon dating, Argon-Argon dating, and Rubidium dating
[I'm writing this without any refs - so this last one might be wrong]).
Usually the radioactive 'clocks' for these elements are started when the
elements are deposited by a volcanic eruption (usually in the form of ash).
These elements have _much_ longer half-lives than Carbon, and in some cases
can be cross-referenced if more than one of these elements is present in
avolcanic tuft.  There are other methods for dating fossils, such as
themolumenescence.

    Allan Edels


-----Original Message-----
From: Haist, Brandon <brandonc@advant.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Saturday, December 05, 1998 6:18 PM
Subject: Radiocarbon Dating


>
>A little while ago this website was posted:
>
>http://www.teleport.com/~swc/carbon/radiocar.htm
>
>This site deals with radiocarbon 14 dating, and says the following:
>
>"Whereas once taxonomists
>were unsure of the chronology of fossils. Now
>taxonomists have a highly reliable method by which
>to place fossils In their appropriate order with
>respect to time. "
>
>Isn't this wrong?
>
>In "The Handy Science Answer Book", compiled by the Science and Technology
>Department of the Carnegie Library of Pittsburgh, it is said on page 197 to
>198:
>
>"[carbon 14] Its half-life of 5,730 years made it useful for measureing
>prehistory and events occurrring within the past 35 to 50 thousand years.
>...  ...  In this way, the age of an animal or plant 50,000 yrears old or
>less can be determinded."
>
>The book goes on to tell about other methods of dating that go farther
back,
>but the point is that unless the "fossils" 50,000 years or less, then
carbon
>14 doesn't work.  I hope that the site was refering to recent human
history,
>not dinosaurs or other fossils.
>
>Would finds found in the carbon 14 timespan be called something else
besides
>"fossils"?
>~Brandon Haist
>
>
>
>