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Radiometric Dating

Radiometric Dating Radioactive elements (like uranium ) in minerals act like accurate atomic clocks • the clock works because radioactive elements decay ( or break down) at a very regular rate • rate of decay is not affected by temperature , pressure, or any natural process

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Radiometric Dating

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  1. Radiometric Dating Radioactive elements (like uranium) in minerals act like accurate atomic clocks • the clock works because radioactive elements decay(or break down) at a very regular rate • rate of decay is not affected by temperature, pressure, or any natural process • a half-life is the period of time it takes for 1/2 of a sample of a radioactive element to decay into its daughter products examples: carbon-14 has a 5730 year 1/2 life uranium-238has a 4.5 billion year 1/2 life • by comparing the amount of the radioactive parent to its daughterproduct, the number of half lives, and thus the age, can be determined

  2. • How the clock is set to zero: • for minerals: minerals in igneous rock form only with a specific crystal structure and chemical formula example: uraninite (UO2) can’t form with lead in its crystal structure, only uranium and oxygen • so when a mineral forms, the radioactive isotope is 100%, daughter product is 0% soany daughter product found in the crystal must be due to radioactive decay

  3. • for living things, the radiocarbon dating method is used • most carbon in nature is carbon-12, but a small percentage is radioactive carbon-14 • carbon-14 is continuously made as cosmic rays collide with atmospheric nitrogen • living things take in both carbon-12 and carbon-14 throughout life • at death, carbon intake stops and the carbon-14 in the tissue decays into nitrogen-14 • the carbon-12 to carbon-14 ratio in a sample is then compared to living things; the less carbon-14, the older the sample

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