Rain falls toward glowing ground and vanishes into steam. Try to picture a whole ocean still trapped in the sky. The rock below is too hot to hold it.
Steam keeps heat in, like a blanket. But some warmth escapes into space, and slowly the sky cools. At last, drops can reach the ground and stay there. Each drop takes steam out of the air, thinning the blanket so more heat can escape. More rain follows.
This is where the storm becomes an ocean. The chapter uses about 1,000 years for the rainfall, from a model of how fast Earth can shed heat. Turning steam to water releases heat too, so the sky cannot empty all at once.
The rain changes the ground as it falls. Carbon dioxide mixed with water makes a weak acid, like the one in a fizzy drink. It eats at fresh rock and washes dissolved minerals into the sea.
Scientists still argue about how sour that early ocean stayed. And no rock records the whole storm or its exact starting day. Ancient crystals give us clues that water was there; the rainfall comes from physics and models. Beneath the thinning sky, water can finally pool.
