Carbon Dating

We've all heard of carbon-dating; it's practically a household word these days. No, it's not when two carbon atoms start to date (although, that's super cute), but rather, the scientific method that allows archeologists to declare how old stuff is. Stuff could be anything, a bone, dinosaur poop, a clay pot.

There are a few isotopes of carbon on Earth. The most abundant and stable one is Carbon-12, which is 99% of all the Carbon on the planet. Carbon-14 is formed on Earth as high energy cosmic-rays from outer space interact with our atmosphere, where carbon dioxide resides. The most prominent production of C-14, accounting for 99.63% of it, occurs as thermal neutrons interact with nitrogen, as seen here:

On Earth, both C-14 and C-12 are absorbed by living organisms in the form of carbon dioxide, CO₂. Throughout its life, a living organism maintains a steady ratio between these two isotopes of carbon, with an extremely small percentage of C-14.

A living organism will also keep a balanced amount of C-14 throughout its life. Remember that C-14 is an unstable isotope with a half-life of t_1/2 = 5,730 years. It β-decays back to the stable N-14.

C-12, on the other hand, is a stable isotope. When an organism dies, its levels of C-12 remain the same, however, since it's well, dead, it no longer intakes C-14 and C-14 decays, so the ratio of C-12 to C-14 begins to change at death.

By measuring the ratio of C-12 to C-14 and knowing the half-life of C-14, scientist calculate the age of a specimen. That's cooler than Indiana Jones, right there.