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Comment: 05:53 - 07:05 (01:12)
Source: Annenberg/CPB Resources - Earth Revealed - 2. The Restless Planet
Keywords: "David Stevenson", "planetary formation", planet

Our transcription: The cloud of material from which the planets formed started out as being mostly gas with a small amount of dust.
That dust was very fine indeed, but the particles collided with each other, and during those collisions they stuck with each other, so that materials started to coagulate into still bigger bodies, so you have to imagine that we went from dust particles all the way up to objects that were kilometers across.
Those objects were colliding with each other making still bigger bodies, so that we think of the formation of solid planets like the Earth as being a hierarchical process, a process that starts off with very small things, very large in number, towards intermediate sizes things, smaller in number, and eventually ending up with a very small number of large objects.
As an intermediate stage in this process, we could imagine that the region where the Earth formed contained hundreds of objects that were about the size of the Earth's moon.
Most of those objects, then, coalesced to make a single planet, the Earth.

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