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How It Works: Carbon has 3 isotopic forms: Carbon-12, Carbon-13, and Carbon-14.The numbers refer to the atomic weight, so Carbon-12 has 6 protons and 6 neutrons, Carbon-13 has 6 protons and 7 neutrons, and Carbon-14 has 6 protons and 8 neutrons.Limitations and calibration: When Libby was first determining radiocarbon dates, he found that before 1000 BC his dates were earlier than calendar dates.He had assumed that amounts of Carbon-14 in the atmosphere had remained constant through time.Rodents, for example, can create havoc in a site by moving items from one context to another.
Plants are not the only organism that can process Carbon-14 from the air.In fact, levels of Carbon-14 have varied in the atmosphere through time.One good example would be the elevated levels of Carbon-14 in our atmosphere since WWII as a result of atomic bombs testing.Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.So every living thing has a certain amount of radiocarbon within them.
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Looking at the graph, 100% of radiocarbon in a sample will be reduced to 50% after 5730 years.