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Comment: 16:45 - 17:48 (01:03)
Source: Annenberg/CPB Resources - Earth Revealed - 2. The Restless Planet
Keywords: "water vapor", volcano, comet, "David Stevenson", ocean

Our transcription: Volcanic activity also released vast amounts of water vapor.
Many geologists argue that this condensed to form the world's oceans.
Recent work, however, suggests that factors other than volcanism may also have played a role.
Another very interesting possibility is that the water came in comets, in bodies that formed in the far reaches of the Solar System and were scattered into earth crossing orbits.
We now see, of course, how much that crossed the Earth's orbit like Halley's Comet, and, very really, objects like this even hit the present Earth.
But in the early history of the Solar System, these collisions would have been more frequent, and the amount of water on the Earth, although we might think of it as being large because we live on the surface of the Earth, is actually quite small compared to the total mass of the Earth.
So you don't need a very large number of comets to explain all of the water that we see in the Earth's oceans.

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