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Earth is a water planet, but where did it all come from?

Currently, planetary scientists are taught that water wasn't really present when our planet was forming. We thought that Earth was

like pretty bone dry to begin with. So it had to be delivered from somewhere else in the solar

system. That's Michael Wong, an astrobiologist and planetary scientist at Carnegie Science here in Washington, D.C.

I was taught that basically the rocky materials that formed where Earth is now at its distance from the sun,

those materials were very dry. They didn't have a lot of water in them because they were too close to the sun and too hot to retain any H2L.

But the thinking goes, somewhere farther out in our solar system, there are objects with water in the form of ice.

And that could have hauled ice to us at some point.

And so there was kind of this debate over whether or not it was mostly asteroids or mostly

comets that were responsible for delivering, shipping Earth's water late on in the game.

But that's not the only hypothesis in the race.

For years, some scientists have been disagreeing in a healthy way with each other

about whether another hypothesis could be the true one. I think people had published these

very theoretical papers about planets just being naturally imbued with water or generating

their water themselves through reactions between hydrogen atmosphere

and the metals in the planet.

But I don't think anybody really took that very seriously, at least until now.

Today on the show, choose your fighter for the origin of water on earth.

Where did it come from?

Was it always here?

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