Potassium argon kar dating of volcanic sediments is

There's another layer of volcanic rock right over there. So they're all going to have a certain amount of potassium-40 in it.

But what's neat about argon-40 is that while it's lava, while it's in this liquid state-- so let's imagine this lava right over here. And so what you can do is you can look at the ratio of the number of potassium-40's there are today to the number that there must have been, based on this evidence right over here, to actually date it.

And what's really interesting to us is this part right over here. And it might already have some argon-40 in it just like that. And that's why the argon-40 is more interesting, because the calcium-40 won't necessarily have seeped out. You know that this argon-40 is from the decayed potassium-40.

Because what's cool about argon, and we study this a little bit in the chemistry playlist, it is a noble gas, it is unreactive. And you know that it has decayed since that volcanic event, because if it was there before it would have seeped out.

And in the next video I'll actually go through the mathematical calculation to show you that you can actually date it.

And the reason this is really useful is, you can look at those ratios.

Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work! This dating method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.