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Why Is Earth So Dry?

17 Jul 2012, 17:00 UTC
Why Is Earth So Dry?

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With large swaths of oceans, rivers that snake for hundreds of miles, and behemoth
glaciers near the north and south poles, Earth doesn't seem to have a water shortage.
And yet, less than one percent of our planet's mass is locked up in water, and even
that may have been delivered by comets and asteroids after Earth's initial formation. Astronomers have been puzzled by Earth's water deficiency. The standard model
explaining how the solar system formed from a protoplanetary disk, a swirling disk of
gas and dust surrounding our Sun, billions of years ago, suggests that our planet should
be a water world. Earth should have formed from icy material in a zone around the Sun
where temperatures were cold enough for ices to condense out of the disk. Therefore,
Earth should have formed from material rich in water. So why is our planet comparatively

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