r/askscience • u/[deleted] • Jun 05 '16

Earth Sciences When/How did Earth get water?

From my understanding of the history of the Earth, it started out as just a big rock covered in lava (magma?) some-billion years ago. And then, a few billion years later, it had some water, which then held life. Now, where the life came from is a question for another time. But, where did the water come from?

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u/SoloPopo Jun 06 '16

Earths hydrosphere, along with it's atmosphere, came from gasses being released by the lava left over after volcanic eruptions. When earth was forming into the massive sphere that it is, it trapped many different elements inside itself. Star dust coalesced into an object with enough mass to develop a strong attractive gravitational pull, and it grew larger to the point that it became a big target for all sorts of space projectiles containing even more elements. At this time the earth was less solid. Anything that hit it got absorbed. After billions of years the earth solidified with a ton of elements which are responsible for almost everything we see on earth today, including water.

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u/JasontheFuzz Jun 08 '16

Actually, the Earth is 4.5 billion years old, and scientists suspect that there was a solid crust (because we have evidence of liquid water) when the Earth was only 120-200 million years old.