Carbon Dating

Question

I understand that it works by measuring the amount of carbon 14 which has different amounts depending how old the matter is. But how is it known how much carbon 14 there was that long ago? Is it just that is takes x years for this much to decay so 104 x yea ago they figure it out on a simple graph?

In:

Answer 1

Carbon Dating is measuring the **ratio** between Carbon 14 and Carbon 12.

See, when things are “alive”, they acquire Carbon 14 from the atmosphere (or from their diet!) until they’re at equilibrium. Critters and organic compounds have the same amount of C14 as their environment.

When they die, that C14 starts to degrade. However! C12 is a **stable** element, meaning it doesn’t really degrade over time. So we can compare the current C14 next to the current C12 and figure out a “maximum” C14 content (because living things have about 1.25x more C14 than C12).

We do have to use **some** guesswork regarding the total amount of C14 in an environment over time, because that can change quite a lot. That’s why carbon dating gives a large variable, “100,000 to 300,000 years old” for example.

For objects, we can only really use C14 dating on things that were once alive, like leather, sinew, bone, plant fibers, and stuff like that. Lucky for us, a lot of artifacts we find through archeology have those things in them! We might find a clay bowl alongside a bone spoon, that Bronze Age sword might have a leather grip or carrying strap!

For things that have absolutely no organic components, we use a different kind of dating. Sometimes we’ll use Uranium lead dating, which works by examining zircon crystals inside of rocks and other minerals. We know a lot about zircon crystals, and they’re **in basically all natural minerals**, so that makes it really useful for dating.

Uranium lead dating is super useful because it checks two different radioactive components, one that degrades into lead (pb206) and one that degrades to a slightly different thing from lead (pb205). They have different half lives, so when both calculations come up with the same “life estimate”, we know we’re on the money.