Today, scientists attempt to determine the age of dead organisms by measuring the ratio of C-12 to C-14, by comparing it to an assumed but unobserved initial ratio, and determining how long it would take to get from the assumed but unobserved initial ratio at an assumed but unobserved rate of decay.

Here are the key assumptions: There is one fact that makes it highly unreasonable to believe that the proportion of C-14 to C-12 was the same in the past as it has been in recent history: It is not in equilibrium.

The C-14 combines with oxygen to form carbon dioxide, plants take in the radioactive carbon dioxide, animals eat the plants, and so all living things on earth have a constant level of C-14: roughly one atom in a trillion.

When an organism dies, it stops taking in carbon-14 and the carbon-14 it already contains starts to decay.

Carbon-14 dating is a radiometric dating technique used to deduce the approximate age of organic remains by measuring the quantity of C-14 isotopes in the sample and comparing them with current atmospheric levels.

C-12 and C-14 are two different isotopes of carbon.

Twenty half-lives, or 114,000 years, will reduce the original abundance of C-14 by about a million.

C-12 is stable, meaning it does not decay into other elements over time. It is formed when cosmic radiation strikes N-14 (Nitrogen), converting it into C-14, and it decays back into N-14, with a half-life of 5730 years, meaning that for any sample of C-14, half of it will decay back into N-14 every 5730 years.

Carbon-14 is used to date dead plants and animals, because plants and animals incorporate C-14 into their bodies by eating, drinking, and breathing in an environment containing C-14.

At this point, and for the years following, the C-14 in the sample begins to decay back into N-14, while the C-12 does not decay.

Both C-14 and C-12 are lost as the body decays, but they are lost proportionally, so that the proportion of C-14 to C-12 decreases slowly for thousands of years after the death of the organism.