Hey everybody, quick heads up. Next week, the shortwave science movie club is back.

We'll be talking about the science in the 1997 sci-fi drama contact.

So, if you can, try and see the movie before the episode drops next week.

Alright, on with today's show.

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 rift 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 plate tectonics.

Plate tectonics.

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 plate tectonics was because our high school did this nerdy

ocean science competition.

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