Excerpt from newsok.com
Water was
present in great quantity 4.6 billion years ago when the planets of our
solar system took shape. Venus, Earth and Mars formed with copious
amounts of water. But Venus’ 900-degree atmosphere boiled it away and
broke it down into its constituent parts or combined it with sulfur
dioxide gas to create the planet’s thick sulfuric acid cloud cover.
Mars’ small size meant weak gravity, so its atmosphere leaked into
space, and its water evaporated, which it does with no air pressure
above it, and also leaked into space.
Strong, active volcanism, aided by massive asteroid impacts boiled
into space most, if not all, of remaining water on all three planets.
And yet, today, three quarters of Earth is covered with water. Where did
it come from?
For years, astronomers assumed that comets, the most common
water-bearing objects in our solar system, brought the water to Earth.
But comets formed much farther from the sun than Earth did. The isotopic
composition of water differs with distance from the sun.
Thanks to the Rosetta spacecraft, we now know that cometary water
doesn’t match terrestrial water. But asteroid water does. Today,
asteroids are quite parched, but 4.5 billion years ago, when many
asteroids impacted the planets and moons of the inner solar system,
water represented a much larger fraction of their mass. And, it appears,
they are the source of Earth’s oceans.
It turns out that asteroid impacts that, today, could wipe out life
on Earth, made it possible for life to flourish here in the first place
by providing the precious water.
Source Article from http://feedproxy.google.com/~r/AscensionEarth2012/~3/AVlXV67VI_A/scientists-deem-asteroids-source-of.html
Scientists Deem Asteroids Source of Earth's Oceans
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