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Because of gravity, 4 billion 600 million years ago, some particles began to accumulate a larger object, the earth.
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The moon was formed because 4 billion 500 million years ago, a Mars sized planet collided with the earth, and some of the remaining fragments gathered together.
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450 million to 4 billion years ago, the so-called cooling of the planet was that the heat in the earth began to slow down as time went on.
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The so-called "late heavy bombardment" is that many comets and asteroids hit the earth 4 to 3 billion 800 million years ago.
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The core of the molten iron in the middle of the earth is 150 million to 1 billion years ago.