If you ever wondered why nuclear tests are now performed underground, this is why.
Most radiocarbon dating today is done using an accelerator mass spectrometer, an instrument that directly counts the numbers of carbon-14 and carbon-12 in a sample.
is a term for radiocarbon dating based on timestamps left by above-ground nuclear explosions, and it is especially useful for putting an absolute age on organisms that lived through those events.
And yet we know that "radiocarbon is forming 28-37% faster than it is decaying," which means it hasn't yet reached equilibrium, which means the ratio is higher today than it was in the unobservable past.
We also know that the ratio decreased during the industrial revolution due to the dramatic increase of CO produced by factories.
C-14 is produced in the upper atmosphere when nitrogen-14 (N-14) is altered through the effects of cosmic radiation bombardment (a proton is displaced by a neutron effectively changing the nitrogen atom into a carbon isotope).
The new isotope is called "radiocarbon" because it is radioactive, though it is not dangerous.
Plants and animals naturally incorporate both the abundant C-12 isotope and the much rarer radiocarbon isotope into their tissues in about the same proportions as the two occur in the atmosphere during their lifetimes.
When a creature dies, it ceases to consume more radiocarbon while the C-14 already in its body continues to decay back into nitrogen.
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.
But when gas exchange is stopped, be it in a particular part of the body like in deposits in bones and teeth, or when the entire organism dies, the ratio of carbon-14 to carbon-12 begins to decrease.
It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes and human activities.