You're listening to shortwave from NPR.

So imagine you're floating over the earth, say a couple billion years ago.

What would you recognize?

Well, you would see large bodies of water.

We don't know how much land there was back then, but there was definitely some.

If you ask Roger Foo, it might look surprisingly familiar.

So you would probably see the same kinds of mountain belts, valleys and riff basins that you might see today.

Roger's a professor in the Department of Earth and Planetary Science at Harvard University.

He says, you'll also notice, Earth isn't covered in craters like other planets are.

That difference stems from the fact the Earth's surface is constantly recycling itself through the action of platechtonics.

We all remember learning about it.

Kind of.

Roger, I'm a microbiologist and I have to be honest with you.

I read your paper and I was like, oh buddy, you are not in biology anymore.

The only reason I know about platechtonics was because our high school did this nerdy ocean science competition.

Like this kind of like buzzer like jeopardy style and we all like kind of read textbooks in our spare time.

That's what spare time is for.

Eventually, all that extra book reading paid off because Roger's lab recently published a study showing

that the Earth's tectonic plates started shifting hundreds of millions of years earlier than we thought.

Which is important because by knowing when those shifts happened.

We can say something more about the environment in which life evolved.

So today in the show Roger Foo tells us how we know what was happening with Earth's tectonic plates billions of years ago.

...