Earth may have forged hundreds of oceans’ worth of water deep within its own atmosphere during its volatile planetary formation, according to new research published in Nature Geoscience.
The study challenges decades of scientific debate suggesting our planet relied entirely on comets, meteorites, or icy pebbles delivering water from the outer solar system. Instead, researchers at The University of New Mexico demonstrate that water could have been produced directly through chemical reactions between the rocky materials building the young Earth and its surrounding gases.
As countless small pieces of rock accumulated through pebble accretion to form the growing planet, Earth gathered a dense, hydrogen-rich atmosphere characterized by extreme temperatures and pressures. When silicate rocks fell through this fiery environment, iron oxide within the material reacted rapidly with atmospheric hydrogen.
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.
Zachary Sharp, professor and director of Earth and Planetary Sciences at The University of New Mexico
To investigate whether this planetary growth process could generate water, researchers recreated the extreme conditions of early Earth in the laboratory. The experimental team was led by graduate student Susmita Garai, alongside Sharp and Peter Olson.
The team heated silicate rock samples in streams of hydrogen—and, for comparison, helium—at temperatures ranging from 1,200°C to 1,400°C. The experiments lasted anywhere from 15 minutes to three hours. When exposed to hydrogen, nearly 80% of the iron oxide in the rocks transformed into metallic iron, producing water vapor in just minutes. In contrast, the researchers observed no such reaction when using helium.
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.
Zachary Sharp, professor and director of Earth and Planetary Sciences at The University of New Mexico
The discovery offers a fresh explanation for how our planet acquired an essential ingredient for life. Because the idea of pebble accretion has been around for the last decade, the new findings suggest that water generation may be a built-in feature of rocky planets throughout the cosmos.
“And now we see that it also can explain why our planet is habitable. By extension, it is reasonable to expect that other Earth-sized bodies circling other stars would also have water and possibly life,” Sharp said. Additional research will be required to establish exactly how much of Earth’s current water supply originated via this atmospheric mechanism versus external deliveries from meteorites and comets.
