Why measure the carbon-14 works? Are the carbons atoms create some manner in the life of the organism now dead and fossilized? How do we know that the atoms weren’t there before?
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Carbon 14 in the atmosphere (up until the nuclear bombs) existed in a natural balance – a specific ratio of c-14 to overall carbon. This is from a process in the upper atmosphere involving cosmic rays.
So, the ‘count’ starts when that carbon is absorbed from the atmosphere by the plant, at which point it is removed from the equilibrium and its carbon 14 is no longer being regenerated.
The idea behind carbon dating (measuring carbon 14 isotopes) goes on the line that when a carbon based life form is alive, it’s constantly consuming small doses of carbon-14 in amongst all the regular carbon-12, so the “average” baseline of carbon-14 is about steady. Once something dies, it stops taking in carbon at all, so the level of carbon-14 starts to drop as it decays to non radioactive atoms. Since carbon-14 decays at a known rate, an extrapolation can be done, basically working backward from the amount there right now to what starting average baseline is, giving an estimate of age. It’s definitely not 100 percent though, as things like air pollution, both man made and from things like volcanic eruptions, can interfere with the process.
Carbon has two forms, carbon-14 and carbon-12. Carbon-14 will decay to carbon-12 naturally and consistently. Through observation, we know that if we have a billion c-14 atoms, after a certain time, half of them will decay to c-12 (half-life).
Carbon-14 is created in the atmosphere and there’s a consistent ratio of 14/12 in atmospheric carbon. Living beings take in this carbon from the atmosphere. Plants by photosynthesis, animals by eating plants. So animals always have the same 14/12 ratio as the atmosphere when they’re alive. As soon as they die, they stop taking in atmospheric carbon and as c-14 changes to c-12, the ratio of 14/12 in their bodies drops. So by measuring the 14/12 ratio of something dead, we can tell very accurately how long ago it died.
Carbon 14 is almost like carbon 12 (which is normal carbon carbon), except it is radioactive.
While an organism is living, and taking in air, there is a certain amount of carbon in that air (usually in the form of carbon dioxide). A specific tiny ratio of that carbon will be carbon 14.
When an organism stops taking in carbon from the environment, the amount of radioactive carbon is locked. There will be no more added.
Carbon 14 decays into carbon 12 over time.
So when scientists measure the ratio of carbon 14 to carbon 12, the older the sample is, the less carbon 14 will be in it.
At some point there is so little carbon 14 we can’t even measure it, and we have to use a different element for dating. This is a very long time, several tens of thousands of years.
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