How does carbon dating work?
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Almost all carbon in the atmosphere is carbon-12. This is what you would think of as “normal” stable carbon. However, there is _some_ carbon that is carbon-14 – a radioactive isotope of carbon that has a half-life of 5,730 years. This means that after 5,730 years, half of the carbon-14 in something will decay into nitrogen-14.
When something is alive, it will have an expected ratio of carbon-12 to carbon-14 (based on normal concentrations for that time period). However, once that thing dies, the carbon inside the thing is “fixed.” We can use that fact to look at the ratios of carbon-12 to 14 to determine how much of the carbon-14 has decayed, which will tell us how long ago the thing died.
It only works for things that are less than ~50k years old; after that point, too much of the carbon-14 has decayed and we have to use other dating methods.
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