Early human carbon dating
It is then incorporated into all living organisms by means of the food chain.After an organism dies, its level of carbon-14 gradually declines at a predictable pace, with a half-life of about 5,730 years.Radiocarbon decays slowly in a living organism, and the amount lost is continually replenished as long as the organism takes in air or food.
Radiocarbon present in molecules of atmospheric carbon dioxide enters the biological carbon cycle: it is absorbed from the air by green plants and then passed on to animals through the food chain.Archaeologists precisely measure levels of the isotope in organic remains.Knowing the halflife, they back calculate how much time must have passed since the remains had levels identical to living organisms.It has resulted in artificially high levels of carbon-14 in plants and animals living in the past 60 years.The forensic use of carbon-14 measurement does not rely on the slow decay process.
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Since then, atmospheric carbon-14 levels have been declining as the radiocarbon is soaked up by the oceans and the biosphere.