New research from the University of New Mexico suggests rocky pebbles reacting with hydrogen in Earth's early atmosphere could have produced hundreds of oceans' worth of water during the planet's formation.
New research published in Nature Geoscience suggests Earth may have created a substantial amount of its own water as the planet was forming, rather than relying entirely on comets, meteorites, or other objects to deliver it from space.
Researchers at The University of New Mexico recreated extreme conditions believed to have existed during Earth's formation. The study was led by graduate student Susmita Garai, along with Zachary Sharp, professor and director of Earth and Planetary Sciences, and Peter Olson.
The team exposed samples of silicate rock to temperatures ranging from 1,200 to 1,400 degrees Celsius. They conducted experiments using flowing hydrogen gas and repeated the tests with helium to provide a comparison. Each experiment ran for between 15 minutes and three hours.
When the rocks were heated in hydrogen, almost 80% of their iron oxide was transformed into metallic iron, with water vapor produced during the reaction. The researchers did not observe the same reaction when helium was used instead of hydrogen.
"We had suspected and hoped that we would produce iron metal and water in our reduction experiments, but we really had no way of knowing how fast and how much. We were quite surprised to find that extrapolation of our work suggests that hundreds of oceans' worth of water were likely produced in this way," said Sharp.
The study proposes that during pebble accretion, rocky pebbles falling through a dense, hydrogen-rich atmosphere could have triggered a chemical reaction in which hydrogen reacted with iron oxide inside silicate rocks, transforming the iron oxide into metallic iron while releasing water vapor.
"Previous ideas about the source of water to Earth rely on an external source, such as comets or meteorites. Here we show that virtually any Earth-sized planet should have water by this newly identified mechanism," explained Sharp.
The researchers caution that the experiments show rocky material can generate water under conditions resembling those of the early Earth, but they do not establish how much of Earth's present water supply was actually produced this way. Additional research will be needed to determine the contribution of this mechanism compared with water delivered by comets, meteorites, and other sources.
If rocky planets around other stars develop similarly hot, hydrogen-rich atmospheres during their formation, they might also produce substantial amounts of water as rocky material accumulates. This could mean that water, and potentially life, could be common throughout the universe.
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