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They have the same ratio of carbon-14 to carbon-12 as the atmosphere, and this same ratio is then carried up the food chain all the way to apex predators, like sharks.For example, in 1991, two hikers discovered a mummified man, preserved for centuries in the ice on an alpine mountain.A detailed description of radiocarbon dating is available at the Wikipedia radiocarbon dating web page.This plot shows the level of carbon-14 in the atmosphere as measured in New Zealand (red) and Austria (green), representing the Northern and Southern Hemispheres, respectively.

Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out.

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