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The remains of a mammoth were recently unearthed in a Michigan farmer’s field [1]. This find could provide new information on the activity of early humans in the area, experts at the University of Michigan have said.

The remains of the animal, thought to be 11,700-15,000 years old, show “evidence of human activity.” How do the scientists determine this age?

[1]: www.youtube.com/watch?v=jwsCKW8WJm8

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Organic material (plants and animals) contains carbon.

Carbon has three main isotopes: carbon 12, 13 and 14. Carbon 14 is radioactive, with a half life of 5730 years.

Carbon 14 is continuously created in the atmosphere by cosmic rays hitting nitrogen. The nitrogen atoms lose a proton when struck by cosmic rays, turning the affected nitrogen atom into an atom of carbon.

The carbon 14 then reacts with oxygen in the atmosphere to create carbon dioxide. Plants taken in the radioactive carbon dioxide along with non radioactive carbon dioxide. Plant eating animals take in the radioactive carbon when they eat plants and meat eating animals take in radioactive carbon when they eat other animals.

When a plant or animal dies it stops exchanging carbon with the environment and it dies with a certain amount of radioactive carbon 14.

By measuring how much carbon 14 is contained in a specimen and knowing the half life of carbon 14, scientists can calculate when an animal died.

Due to the half life of carbon 14 being 5730 years, carbon 14 dating can only reliably be used for dates up to 50 000 years old.

More details about carbon 14 dating can be found here.

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    $\begingroup$ You should probably mention other forms of radiometric dating as well, which have different thresholds of reliability. $\endgroup$ – called2voyage Oct 6 '15 at 15:33

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