radiodate - BIOLOGICAL SCIENCE 102 ANIMAL BIOLOGY...

BIOLOGICAL SCIENCE 102 – ANIMAL BIOLOGY – VOCABULARY & NOTES 1
¾ RADIOMETRIC DATING
ISOTOPE = an element with a different number of neutrons as compared to the parent element
RADIOACTIVE ISOTOPE = an isotope that gives off energy and decays into another isotope
A breakthrough came with the discovery of radioacticity at the beginning of the 1900s.
Scientists discovered that rocks could be timepieces -- literally. Many chemical elements in
rock exist in a number of slightly different forms, known as isotopes. Certain isotopes are
unstable and undergo a process of radioactive decay, slowly and steadily transforming,
molecule by molecule, into a different isotope. This rate of decay is constant for a given isotope,
and the time it takes for one-half of a particular isotope to decay is its radioactive half-life. For
example, about 1.5 percent of a quantity of Uranium 238 will decay to lead every 100 million
years. By measuring the ratio of lead to uranium in a rock sample, its age can be determined.