Why Is
Earth So Dry?
JULY 17,
2012: 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 dry?
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