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q |
Solar luminosity was much
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weaker (~30%) in the early part
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of Earth’s
history (a faint young
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Sun).
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q |
If Earth’s albedo and greenhouse
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effect remained unchanged at that
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time, Earth’s mean surface
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temperature would be well below
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the freezing point of water during
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a large portion of its 4.5 Byr
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history.
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q |
That would result in a “snowball”
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Earth, which was not evident in
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geologic record.
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