The Ice That Fell From Nowhere

You are standing at the edge of a young ocean, and every drop of it arrived from somewhere else. Not from underground springs, not from the rock sweating itself dry — from out there, in the dark, where the Sun's warmth barely reaches. Billions of tonnes of ice, locked inside slow-moving mountains of stone, fell inward over millions of years and shattered against the early Earth. The heat of each impact flash-boiled the ice to steam. The steam cooled. It rained. And rained. And rained, for longer than the whole age of complex life has since lasted, until the basins filled and the first ocean breathed itself into existence.

The name for those stone mountains is comets. And here is the thing that nobody agrees on yet: we don't know if they brought enough. The math keeps coming up short. There may have been a second source — asteroids, wetter and darker than comets, arriving in their own long procession. Perhaps both. Perhaps something else entirely.

What we do know is this: somewhere inside the water in your body is hydrogen and oxygen that never belonged to this planet. It was assembled in the cold void between stars, frozen for billions of years, and then delivered here by something that looked like fire in the sky. The sea was not made here. It was posted.