Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.
Dating techniques are procedures used by scientists to determine the age of an object or a series of events.
These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top.
If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
Chronometric techniques include radiometric dating and radio-carbon dating, which both determine the age of materials through the decay of their radioactive elements; dendrochronology, which dates events and environmental conditions by studying tree growth rings; fluorine testing, which dates bones by calculating their fluorine content; pollen analysis, which identifies the number and type of pollen in a sample to place it in the correct historical period; and thermoluminescence, which dates ceramic materials by measuring their stored energy.
Scientists first developed absolute dating techniques at the end of the 19th century.
Geologists often need to know the age of material that they find.The successive layers of rock represent successive intervals of time.Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.Each isotope is identified with what is called a ‘mass number’.When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.