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Rocks and Minerals

Absolute-Age Dating

Absolute-Age Dating
Reading Level
     edHelper's suggested reading level:   high interest, readability grades 6 to 8
     Flesch-Kincaid grade level:   7.59

Vocabulary
     challenging words:    igneous, metamorphic, radioactive, uranium, dating, colored, absolute, short-lived, billion, element, affected, bands, original, mass, lead, positive
     content words:    Mount Saint Helens

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Absolute-Age Dating
By Patti Hutchison 		  
1     Absolute-age dating. No, it has nothing to do with dinner and a movie. Absolute-age dating is way for scientists to tell the exact age of a rock, fossil, or other object. There are several methods used to do this.
 
2     One way is called radiometric dating. This process involves measuring the rate of decay of radioactive isotopes. Isotopes are atoms of the same element that have the same chemical properties. They have different mass numbers. These isotopes are found in igneous and metamorphic rocks. They are also found in fossils and remains of organisms.
 
3     Radioactive substances give off protons (positive particles) and neutrons (neutral particles) at a steady rate. Eventually, these substances change into different elements. The new element is no longer radioactive.
 
4     For example, an isotope of uranium, U-238, will eventually decay into an isotope of lead. This change, over time, is called radioactive decay. In this case, the uranium is called the parent and the lead is called the daughter element.
 
5     Radioactive decay is a constant process. It is not affected by temperature, pressure, or other physical changes. As the number of parent atoms decreases, the number of daughter atoms increases. As scientists measure these changes, they can tell how old a substance is.

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