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%