by Josh Greenberger

Created on: July 25, 2008   Last Updated: July 27, 2008

(July 2008) What are the methods used by scientists to date archeological finds? And do those methods tell the true age of buried organisms?

The method used by scientists to determine the age of archaeological finds is called radiometric dating. It involves measuring decayed radioactive elements and, by extrapolating backward in time, determining the age of an organism.

One element commonly used, in what's referred to as "radiocarbon dating" or "radiocarbon reading," is C-14, a radioactive isotope of carbon, which is formed in the atmosphere by cosmic rays. All living organisms absorb an equilibrium concentration of this radioactive carbon. When organisms die, C-14 decays and is not replaced. Since we know the concentration of radioactive carbon in the atmosphere, and we also know that it takes 5,730 years for half of C-14 to decay (called a "half-life cycle"), and another 5,730 years for half of what's left to decay, and so on, by measuring the remaining concentration of radiocarbon we can tell how long ago an organism died.

Since C-14 can only give dates in the thousands of years, elements with longer half-life cycles (such as Samarium-147, Rubidium-87, Rhenium-187, Lutetium-176, to name a few, with half-life cycles in the billions of years) are used to date what are believed to be older archaeological finds. The procedure is roughly the same; the amount of decay is measured against the initial amount of radioactive material, giving the object's supposed age.

One obvious flaw in this technique is that we don't really know the level of radioactive concentration acquired by an organism which lived before such recorded history. Scientists make a bold assumption that the atmospheric concentration of the radioactive material - carbon or any other element - being measured has not changed since the organism's death.

Another bold assumption made by scientists is that the rate of radioactive decay has remained constant throughout history.

Are these valid assumptions?

Hardly.

In 1994 Otto Reifenschweiler, a scientists at the Philips Research Laboratories in The Netherlands, showed that the radioactivity of tritium could be reduced by 40 per cent at temperatures between 115 and 275 Celsius. That is, under certain conditions, the environment can effect radioactive decay.

In 2006 Professor Claus Rolfs, leader of a group of scientists at Ruhr University in Bochum, Germany, in an effort to reduce nuclear waste radioactivity, has come up a with a technique to greatly speed up radioactive

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