Carbon dating practice questions
In principle, any material of plant or animal origin, including textiles, wood, bones and leather, can be dated by its content of carbon 14, a radioactive form of carbon in the environment that is incorporated by all living things.Because it is radioactive, carbon 14 steadily decays into other substances.But when a plant or animal dies, it can no longer accumulate fresh carbon 14, and the supply in the organism at the time of death is gradually depleted.Since the rate of depletion has been accurately determined (half of any given amount of carbon 14 decays in 5,730 years), scientists can calculate the time elapsed since something died from its residual carbon 14.Uranium 234, a radioactive element present in the environment, slowly decays to form thorium 230.Using a mass spectrometer, an instrument that accelerates streams of atoms and uses magnets to sort them out according to mass and electric charge, the group has learned to measure the ratio of uranium to thorium very precisely.
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For example Carbon 14 has a half life of 5,730 years.
If a sample has 6.25 % of the amount of Carbon 14 present in a living sample then four half lives have passed since the sample died and stopped absorbing Carbon. Carbon 14 has a limited of approximately 50,000 years or less.
But the tree ring record goes no further, so scientists have sought other indicators of age against which carbon dates can be compared.
One such indicator is the uranium-thorium dating method used by the Lamont-Doherty group.