The Cosmic Origin of Our Water

In “Where Did Earth’s Water Come From?” (pdf), the cover story of the January 2011 issue of Sky & Telescope, I investigate the mysterious sources of our water supply. Many scientists think Earth formed with little or no water. But somewhere along the way, Earth picked up oceans full of water. For years, astronomers suspected comets as the main source. But recent evidence points to objects closer to home: asteroids.

No wonder we call Earth the “Blue Planet.” Our home world is the only known planetary object where substantial bodies of liquid water exist at the surface, creating the conditions for life as we know it. In total, oceans and lakes cover 71% of Earth’s surface. Because life is tied inextricably to the presence of water, unraveling the origins of Earth’s oceans could give us tantalizing hints as to how and when life began…

Read the rest at S&T.

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