Earth May Have Made Its Own Oceans: Hundreds' Worth Brewed in Fiery Air

Earth may have made much of its own water while it was still forming, instead of relying on icy comets or meteorites to deliver it, according to new research in Nature Geoscience reported by ScienceDaily. Lab experiments suggest that rocky pebbles reacting with hydrogen in the young planet's scorching atmosphere can produce water in just minutes.

When the researchers scaled up their results to early Earth conditions, their calculations indicated the process could have produced hundreds of oceans' worth of water. It is an extrapolation from experiments, not a direct observation of the early planet.

How scientists thought Earth got its water

For decades, researchers have debated where the planet's water came from. One prominent theory holds that icy material from the colder, more distant parts of the early solar system, including small icy pebbles, traveled inward and supplied it. ScienceDaily noted that scientists have struggled to explain how enough of that material could have reached Earth from so far away, and that questions remain about whether such delivery fits Earth's chemical makeup.

The idea: water made on the spot

The University of New Mexico team tested a different route. Early in Earth's history, countless small pieces of rock gradually came together to build a larger body, a process known as pebble accretion. As the planet gained mass, it could have gathered a dense, hydrogen-rich atmosphere with temperatures and pressures far higher than today's.

Rocky pebbles falling through that atmosphere could then have triggered a chemical reaction. Hydrogen in the gas would react with iron oxide inside the silicate rock, turning the iron oxide into metallic iron and releasing water vapor.

What the experiments showed

The study was led by graduate student Susmita Garai, together with Zachary Sharp, a professor and director of Earth and Planetary Sciences, and Peter Olson. They heated silicate rock samples to temperatures between 1,200 and 1,400 degrees Celsius in flowing hydrogen, and ran the same tests with helium for comparison. Each run lasted between 15 minutes and three hours.

In hydrogen, almost 80% of the rock's iron oxide was converted into metallic iron, with water vapor released.
With helium, the researchers did not see the same reaction, which indicated that hydrogen was key to making the water.

Sharp said the team had hoped to produce iron metal and water but had no way of knowing how fast or how much. He said the results were surprising, and that the extrapolation suggests hundreds of oceans' worth of water were likely produced this way. He also noted that the water we see today may trace back to a "hell-like atmosphere" about 4 ½ billion years ago.

Why it matters: water may be part of how rocky planets form

The finding does not mean comets and meteorites played no role, and it rests on lab work and calculations rather than evidence from the early Earth itself. But Sharp said the team's results indicate that virtually any Earth-sized planet should end up with water through this mechanism.

That would shift the picture of how common water-bearing worlds are. According to the report, the work raises the possibility that other rocky planets across the universe could generate water in similar ways, potentially making habitable worlds more common than previously thought. In this view, water is a natural by-product of how rocky planets are built, rather than something that has to arrive from space.

For everyday readers, the result is a change in the story of where the oceans, rain and rivers around us began: possibly not from distant ice, but from chemistry in the planet's own fiery beginnings.

Around Prague, based on reporting by ScienceDaily

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