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The Hadean era The Hadean era
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The tree of life The tree of life
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The building blocks of life The building blocks of life
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The rise of oxygen The rise of oxygen
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A favorable climate A favorable climate
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Snowball Earth Snowball Earth
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Future habitability Future habitability
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Cite
Abstract
This chapter studies the composition of early Earth, which consisted of two layers: a dense iron-rich core at the center, surrounded by a thick rocky mantle. Gradually, Earth acquired a third layer, a thin basaltic crust on the floor of the ocean. In a few places, the basaltic rock became thick enough to poke up above the waves to form the first primitive continents. As the basalt cooled, it grew denser and eventually became heavier than the mantle below. This configuration was unstable, and in places, the heavy basaltic crust began to sink, or subduct, back into the mantle, where it eventually mixed with rocks deep in Earth's interior. As the basaltic crust subducted, it pulled neighboring material with it, making room for new crust to form and setting up the conditions necessary for plate tectonics—the process of crustal recycling that continues to operate on Earth today.
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