Recent puzzling observations of tiny variations in nuclear decay rates have led some to question the science of using decay rates to determine the relative ages of rocks and organic materials. Scientists from the National Institute of Standards and Technology NISTworking with researchers from Purdue University, the University of Tennessee, Oak Ridge National Laboratory and Wabash College, tested the hypothesis that solar radiation might affect the rate at which radioactive elements decay and found no detectable effect. Atoms of radioactive isotopes are unstable and decay over time by shooting off particles at a fixed rate, transmuting the material into a more stable substance. For instance, half the mass of carbon, an unstable isotope of carbon, will decay into nitrogen over a period of 5, years.
Sincescientists have reckoned the ages of many old objects by measuring the amounts of radioactive carbon they contain.
Many people assume that the dates scientists quote of millions of years are as reliable as our knowledge of the structure of the atom or nuclear power. But the basic concept of radioactive dating, sometimes called radiometric dating, is not difficult, especially since all of us regularly calculate how much time has passed: for example, since our birth, or since we started on a walk. A swimming race is a familiar situation that illustrates the simple principles involved in measuring time.
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