The Day the Oceans Fell

Picture the Earth newly made: not blue, but a hell of molten rock and ceaseless impact, glowing, far too hot to hold a single drop of liquid water. Any water it started with would have boiled off into space. And yet here are the oceans, covering most of the planet. Where did an entire world of water come from?

The leading answer is the strangest one. It fell. For tens of millions of years, as the planet slowly cooled, comets and water-rich asteroids rained down out of the dark — each one a delivery of that ancient interstellar ice — until the water pooled in the lowlands and, at last, stayed. The seas did not seep up from the rock. They arrived from space, one impact at a time, and lay down where they landed.

Which means the rain on your window tonight is the last, gentlest chapter of a bombardment that began four billion years ago. The storm never really stopped. It only slowed.

And if the water came from the sky — did life arrive the same way?