Radiometric dating on fossils
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.
Basically, fossils and rock found in lower strata are older than those found in higher strata because lower objects must have been deposited first, while higher objects were deposited last.
Relative dating helps determine what came first and what followed, but doesn't help determine actual age.
Radiometric dating, or numeric dating, determines an actual or approximate age of an object by studying the rate of decay of radioactive isotopes, such as uranium, potassium, rubidium and carbon-14 within that object. This rate provides scientists with an accurate measurement system to determine age.
Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.Using this technique, called radiometric dating, scientists are able to "see" back in time.Carbon dating is used to determine the age of biological artifacts up to 50,000 years old.Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate.
This is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale.