Spin Google Earth around until you’re looking down at the nation of Oman. Ancient rock in that country is the backdrop for a new study with consequences for our search for life. Water reacts with this rock to produce hydrogen, which could be an energy source for bacteria. Could this happen on other worlds?

Ocean moons like Europa might be our best bet for finding life elsewhere. That’s why NASA is developing the Europa Clipper mission, and the ESA is developing the Jupiter Icy Moons Explorer mission. But detecting life in Europa’s ocean—or the conditions for life—requires specific methods and instruments because the ocean is buried under kilometres of ice. Studies like this one can help inform instrument and mission design and can provide a valuable context in interpreting results from missions to Europa and elsewhere.

The study is “Energetically Informed Niche Models of Hydrogenotrophs Detected in Sediments of Serpentinized Fluids of the Samail Ophiolite of Oman,” and it’s published in JGR Biogeosciences. The lead author is Alta Howells, now at NASA’s Ames Research Center.

An ophiolite is a section of the Earth’s oceanic crust and a piece of the underlying upper mantle. It’s an ophiolite when it’s lifted above sea level and exposed. Ophiolites often become embedded in the continental crust.

The Samail Ophiolite is a well-known geological feature in the Arabian Peninsula. It’s the largest and best-preserved ophiolite in the world, and it formed during Earth’s Late Cretaceous Period, which spanned from about 65 mya to 100 mya. It’s commercially valuable because of its copper ore, but it’s also scientifically valuable because of what it tells scientists about Earth’s geological history.

This image shows the location of the Semail Ophiolite on the eastern corner of the Arabian Peninsula. Image Credit: By Sadeghm2010 at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=54524205
This image shows the location of the Semail Ophiolite on the eastern corner of the Arabian Peninsula. Image Credit: By Sadeghm2010 at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=54524205

The Semail Ophiolite is important in this study because of the portion of the upper mantle rock it contains. Rock from the upper mantle is reduced, which means there’s a lack of oxygen in the rock. There are more ionic sites in the rock that could react with oxygen if it were available. For example, there’s more ferrous iron than ferric iron because there’s not enough oxygen to bond with all of the iron. This results in a mass of rock basically “waiting” for oxygen to fill all of its ionic sites.

This is what’s happening with the Semail Ophiolite. It reacts with water in a process called serpentinization. The serpentinization produces H2, which is molecular hydrogen. The H2 is food for microbes called hydrogenotrophs, which can metabolize it using oxygen and use it as an energy source.

This diagram from the study shows the lithology of the Oman Ophiolite. Study sites are marked with SJA-03, WDA-17, etc. Image Credit: Howells et al 2022.
This diagram from the study shows the lithology of the Oman Ophiolite. Study sites are marked with SJA-03, WDA-17, etc. Image Credit: Howells et al 2022.

There are different types of hydrogenotrophs, and they form hydrogenotroph communities. In this study, the researchers wanted to “… determine geochemical and biological factors that may influence hydrogenotroph community composition …” To do that, they examined the relationship between the “… distribution of hydrogenotrophs among pools of serpentinized fluid in Oman and the
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