Anthropology 2229F/G Lecture Notes - Lecture 14: Carbon-12, E.G. Time
18 Jul 2012
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Document Summary
Lecture 14 part 2 absolute dating: invented by wilfred libby, c-14 most commonly used dating technique in archaeology worldwide, based on natural radioactive decay of isotopes over time (radiometric) Created when cosmic rays come into contact with nitrogen-14 in the upper atmosphere which forms carbon-14. Over time, it reaches an equilibrium (equal amounts being created and decaying) Carbon-14 in a constant ratio in the atmosphere; reacts with oxygen to created carbon dioxide (very tiny percentage of all. Ratio of c-14:c-12 is constant, in specific proportion. Begins to decay after death; changes back to n-14 and is lost. Can only date the remains of living things: assumptions of the technique. Assumes the amount of cosmic rays over time is constant. Stronger magnetic fields deflect cosmic rays, creating less c-14. We know that it varies, e. g. time of sun spots. Burning old carbon, all radioactive carbon would be gone. Increases the amount of carbon-12 in the atmosphere, diluting c-14.
