Why how carbon 14 dating done

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.According to carbon dating of fossil animals and plants, the spreading and receding of great ice sheets lagged behind orbital changes by several thousand years, a delay that scientists found hard to explain. The group theorizes that large errors in carbon dating result from fluctuations in the amount of carbon 14 in the air.Changes in the Earth's magnetic field would change the deflection of cosmic-ray particles streaming toward the Earth from the Sun.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.

Because it is radioactive, carbon 14 steadily decays into other substances.The best gauge they have found is dendrochronology: the measurement of age by tree rings.Accurate tree ring records of age are available for a period extending 9,000 years into the past.Carbon 14 is thought to be mainly a product of bombardment of the atmosphere by cosmic rays, so cosmic ray intensity would affect the amount of carbon 14 in the environment at any given time.#30,000-Year Limit The Lamont-Doherty group says uranium-thorium dating not only is more precise than carbon dating in some cases, but also can be used to date much older objects.

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