Where Earth's water came from is one of the main questions about the origin of life. For a long time it was believed that icy comets or meteorites brought it from outside. But a study published in the journal Nature Geoscience proposes a different scenario: water could have formed directly on the young planet.
Scientists from the University of New Mexico - graduate student Susmita Garai, professor Zachary Sharp and Peter Olson - conducted a series of high-temperature experiments. They heated samples of silicate rocks containing iron oxide to 1200-1400 °C in a flow of hydrogen, and for comparison in a flow of helium. The experiments lasted from 15 minutes to three hours.
The result was impressive: in the hydrogen environment, almost 80% of the iron oxide in the rocks turned into metallic iron, and the by-product was water vapor. In the helium experiments no such reaction occurred - meaning the key is precisely hydrogen.
According to Sharp, previously only external bodies were considered the source of water. "Here we show that virtually any planet the size of Earth should have water thanks to this new mechanism," he explained. The scientists suggest that on the early Earth, surrounded by a dense hot hydrogen atmosphere, droplets of molten rock reacted with the gas, producing water. This process is called pebble accretion - the accumulation of small solid particles onto a growing celestial body.
Extrapolating the results suggests that hundreds of oceans of water could have arisen this way. However, Sharp admits: "It is hard to imagine that water could have appeared 4.5 billion years ago in a hellish atmosphere like that, but it is quite possible that this is how it happened."
An important caveat: this concerns laboratory modeling, not direct observation of the past. Exactly how much of Earth's water arose this way remains to be determined. Nevertheless, the work expands ideas about how water can appear on rocky planets beyond the Solar System - and therefore about the likelihood of life on them.