Dr. Genevieve von Petzinger

You can only do black paint.

It has to be charcoal.

There has to be enough of it that you can get a good sample from it.

Uranium series, because it's uranium, has a very long half-life.

So you can date much further back because of those properties of it.

And what we're measuring specifically is that when limestone, which is what these caves are all made of, when it interacts with water, it melts a little bit and it makes it come down the walls and make those beautiful translucent sheets that are called calcite.

And that's what makes caves look so pretty, right?

Is that sort of the constant dripping down and creating all these pretty white sort of translucent sheets?

Well, in groundwater all over the world, not in scary levels or anything, there's tiny amounts of uranium.

And so as they come down the wall and then they stick, the uranium sticks too.

And what we can measure is the fact that over time, uranium, because it's radioactive, breaks down into other things.

Like there's a type of thorium it breaks into and a type of lead it breaks into.

Those don't occur naturally.

So people can measure how much of these other elements are now on the wall.

And they can backtrack to figure out how long it would have taken for that much to show up.

That's so cool.

Yeah.

And so what we're measuring here is not when it was made, we're measuring when it was covered up.

So it's the minimum age of things.

Isn't that crazy?