Young Earth: water made by a rain of pebbles?
· BehindLines newsroom
What if the Earth had made much of its own water? That is the hypothesis of a study published in Nature Geoscience by a team from the University of New Mexico, presented by ScienceDaily.
The idea: dry pebbles in a hydrogen atmosphere
According to ScienceDaily, the most widespread explanation holds that Earth's water was brought by comets, meteorites or other objects, notably icy materials from the cold, distant regions of the solar system. The researchers explored another route. While forming, the planet grew by piling up small rocky fragments, a process called pebble accretion. It could then have acquired a dense atmosphere rich in hydrogen. In that setting, silicate pebbles falling through the gas could have reacted with it: hydrogen turns the iron oxide in the rock into metallic iron and releases water vapor.
Experiments at very high temperature
The team, led by doctoral student Susmita Garai with Zachary Sharp and Peter Olson, heated silicates between 1,200 and 1,400 degrees Celsius in a stream of hydrogen, then in helium for comparison. Each run lasted from 15 minutes to three hours. According to ScienceDaily, nearly 80% of the iron oxide was converted to metallic iron with water vapor, whereas the same reaction was not seen with helium. The summary published by Nature Geoscience says that water forms in a few minutes or a few hours.
A quantity that raises questions
By carrying their measurements over to early-Earth conditions, the authors calculate, according to ScienceDaily, that this mechanism could have produced the equivalent of hundreds of oceans. Zachary Sharp says he is surprised by this result. He states that practically every planet the size of Earth should have water thanks to this mechanism. ScienceDaily adds that if other rocky planets have hot, hydrogen-rich atmospheres while forming, they could also produce a lot of water, which would make habitable worlds more common than was thought.
Why it matters
These results come from laboratory experiments, later extrapolated to early-Earth conditions. According to ScienceDaily, the forming planet could have had the ingredients to make its own water, rather than depending entirely on a supply from elsewhere in the solar system.