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History of Life: Origins of Life

History of Life: Origins of Life. Chapter 14-3. Age of Earth. The earth is about 4.5 billion years old How did we measure that? Radiometric Dating = calculating the age of an object by measuring proportions of radioactive isotopes. Radiometric Dating.

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History of Life: Origins of Life

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  1. History of Life:Origins of Life Chapter 14-3

  2. Age of Earth • The earth is about 4.5 billion years old • How did we measure that? • Radiometric Dating = calculating the age of an object by measuring proportions of radioactive isotopes

  3. Radiometric Dating • Radioactive Isotope = an unstable form of an element, decays into stable element, gives off energy (radiation) • Ex. Carbon-14 decays into Nitrogen • Ex. Potassium-40 decays into Argon-40

  4. Radiometric Dating • Half-life = the time it takes for half of a radioactive isotope to decay • Ex. K-40 half life is 1.3 billion years

  5. Practice • You are determining the age of an organic object using carbon-14 dating. You know that the half-life of carbon-14 is 5,730 years. If only 25% of the original amount of carbon-14 is left in the object, approximately how old is the object? Carbon-14 half life = 5,730 years When ½ is left then 5,730 years have gone by When ¼ is left then an additional 5,730 years have gone by Therefore the object is 11,460 (5,730 + 5,730) years old

  6. Your Turn To Try • You know that the half-life of K-40 is 1.3 billion years. If only 12.5% of the original amount of K-40 is left in the object, approximately how old is the object? • 3.9 billion years old • If the half-life of a radioactive isotope is 4,000 years, how much of the radioactive isotope in a specimen will be left after 12,000 years? • 1/8 or 12.5%

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