Earth's Oceans May Have Been Cooked Out of Dry Rock

Earth's oceans may have come from rocks with no water in them at all. Drop dry pebbles through a hot, hydrogen-rich atmosphere, a new lab study suggests, and water comes out the other side.

The usual story says Earth's water was delivered by icy comets or water-bearing asteroids. This one says the planet may have made its own.

Researchers at the University of New Mexico simulated what happens when small rocky pebbles fall through the hot hydrogen surrounding a growing planet. In one leading model of planet formation, rocky worlds grow by sweeping up pebbles from sand-grain to pea size. The rock the team used was bone dry, with no water and no water-bearing minerals.

What came out was water, and not just a trace. Scale the process up to a whole planet, the researchers argue, and it could produce oceans.

The chemistry is simple. Hydrogen pulls oxygen out of the iron oxide in the melted rock, leaving iron metal behind and releasing water vapor. In the lab, large amounts of water formed within several hours.

There's a second finding hiding in the results. The iron metal left behind grabs phosphorus and drags it toward the planet's core. That could explain why Earth's mantle holds much less phosphorus than Mars' does. Phosphorus is one of the building blocks of DNA, so where it ended up matters.

This is a lab simulation, not a measurement of early Earth. The idea that rocky planets grow mainly by sweeping up pebbles is still debated, and nobody knows how much of today's ocean this process could account for.

The researchers suggest the same process could hand oceans to Earth-sized planets around other stars. Water might come standard.

Read the full story at Nature Geoscience, September 24, 2026

Hot Take: Making an ocean by accident is impressive. Messing with the ingredient list for DNA in the same reaction is showing off.