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Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.
But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.
Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.For dating minerals and rocks, investigators commonly use the following couplets of parent and daughter isotopes: thorium-232–lead-208, uranium-235–lead-207, samarium-147–neodymium-143, rubidium-87–strontium-87, potassium-40–argon-40, and argon-40–argon-39.The SHRIMP (Sensitive High Resolution Ion Microprobe) enables the accurate determination of the uranium-lead age of the mineral zircon, and this has revolutionized the understanding of the isotopic age of formation of zircon-bearing igneous granitic rocks.Plus, get practice tests, quizzes, and personalized coaching to help you succeed.Free 5-day trial Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes.