If you go walking along the beach or take an ocean cruise, it’s
hard to believe that Earth is essentially a “dry” planet. Barely
0.02 percent of our home planet’s mass is surface water. In fact, our oceans came along a few hundred million years after Earth formed
4.6 billion years ago. Though still debated, astronomers think that
the primeval Earth was most likely irrigated when water-rich asteroids
in the solar system crashed into our planet.
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