Earth’s oceans may have originated from internal chemical reactions rather than external delivery, according to research published in Nature Geoscience.
Scientists at the University of New Mexico found that iron-rich rocks reacting with hydrogen in the early planet’s atmosphere could have generated massive quantities of water during Earth’s formation.
Hydrogen Reactions During Pebble Accretion
The prevailing theory for decades suggested that Earth’s water arrived via icy comets or meteorites from the outer solar system. However, this model faces significant hurdles regarding the transport of such materials and the resulting chemical composition of the planet. Instead, the new study points to a process involving pebble accretion, where rocky material gathered to form the growing Earth.
As the planet gained mass, it developed a dense, hydrogen-rich atmosphere characterized by extreme temperatures and pressures. Researchers hypothesized that silicate rocks containing iron oxide falling through this environment would trigger a reduction reaction. In this process, hydrogen would strip oxygen from the iron oxide, leaving behind metallic iron and releasing water vapor as a byproduct.
Experimental Evidence for Water Production
To test this mechanism, Susmita Garai, Zachary Sharp, and Peter Olson conducted high-temperature experiments. The team exposed silicate rock samples to flowing hydrogen gas at temperatures between 1,200 and 1,400 degrees Celsius for durations ranging from 15 minutes to three hours.
The results confirmed a rapid conversion process. In the presence of hydrogen, nearly 80% of the iron oxide within the rocks transformed into metallic iron, accompanied by the production of water vapor. When the team repeated the experiments using helium as a control, no such reaction occurred, isolating hydrogen as the critical catalyst.
“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, said Sharp.”
Implications for Planetary Habitability
This process is particularly large in scale. By extrapolating their findings to the conditions of the early Earth, the researchers suggest that this mechanism could have produced hundreds of oceans’ worth of water. This challenges the necessity of external water delivery and suggests that water generation is an intrinsic feature of rocky planet formation.
This discovery has broad implications for astrobiology and the search for habitable worlds. If the production of water is a standard consequence of pebble accretion in hydrogen-rich environments, then water-bearing rocky planets may be far more common throughout the universe than previously estimated.
| Experimental Condition | Gas Used | Outcome |
|---|---|---|
| 1,200–1,400°C | Hydrogen | ~80% Iron Oxide Reduction; Water Vapor Produced |
| 1,200–1,400°C | Helium | No Significant Reaction |
Future Research on Terrestrial Water Sources
While the study explains how Earth could have manufactured its own water, the researchers acknowledge that it does not definitively quantify the total contribution of this process versus external sources like comets. Establishing the exact ratio of internally generated water to delivered water remains a key objective for future planetary science.
Zachary Sharp said that the team had suspected and hoped that they would produce iron metal and water in their reduction experiments, but they really had no way of knowing how fast and how much. He added that they were quite surprised to find that extrapolation of their work suggests that hundreds of oceans’ worth of water were likely produced in this way.
The team’s work emphasizes that the habitability of Earth may be tied to the specific physical conditions present during its birth. As scientists continue to evaluate the role of pebble accretion in the development of planetary systems, this chemical mechanism offers a new framework for understanding the distribution of water in the cosmos.
