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Comment: 15:29 - 16:20 (00:51)
Source: Annenberg/CPB Resources - Earth Revealed - 2. The Restless Planet
Keywords: volcanism, atmosphere, "David Stevenson"
Our transcription: The great amount of heat still present in the Earth is demonstrated by active volcanoes.
The volcanoes of today are an awesome spectacle, but more feverish convulsions affected this planet when the Earth was young.
In the present Earth, the amount of liquid rock is really quite small at any time, but in the early Earth a big fraction of the volume would have been molten, so we imagine that the very earliest Earth had an extremely high level of volcanic activity.
When this volcanic activity takes place, gases which are dissolved within the liquid rock are expelled, put into the Earth's atmosphere, and, in this way, we can imagine that the early atmosphere of the Earth was built up by volcanic activity.
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