Anthropology 2229F/G Lecture Notes - Lecture 9: Issf 10 Meter Air Rifle, Radionuclide, C4 Carbon Fixation
9 Feb 2017
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Radioactive isotope potassium-40 (k-40) decays into argon-40 (ar-40) at a known rate. Half life of k-40 is 1. 3 billion years. Volcanic rocks have their k-ar clocks set to zero when they are formed. Measure the amount of ar-40 in a sample to estimate date that rock formed. The more ar-40 relative to k-40 the older the sample. Works with much smaller samples: rock crystals. Convert the potassium in rock crystals to argon-39. Measure a-39 and a-40 as a proxy estimate of the ratio of potassium-40 to argon 40 and calculate the date. Based on the decay of the radioactive isotope carbon-14: half life is 5730 years. 14 left in a sample: compare to the normal ratio of c-12 to c-14 found in living plants and animals. Avoid contamination: carbon samples must be carefully collected, stored and cleaned. Indicates 68% chance that the age of the sample with lie within one standard deviation.
