Did the chemical components necessary to create water on Earth come from space or already exist here? One prevailing notion holds that asteroids containing either water of its building blocks bombarded the planet. But now, a team of researchers have produced evidence that those building blocks were here since early in the planet’s history, according to a study published in the journal Icarus.
Pinpointing when and where Earth’s hydrogen is an essential key to understanding how life arose on the planet. Without hydrogen, there’s no water, and without water, life can’t exist here.
Water Origins on Earth
Ironically, researchers turned to a meteorite containing hydrogen to prove that such former bodies did not provide the H2 ingredient of water’s H2O recipe. They examined a rare type of meteorite — known as an enstatite chondrite — that was built similarly to early Earth 4.5 billion years ago and the team discovered hydrogen present in the chemical. The logic is that if this material resembling early Earth’s composition can contain hydrogen, so too could the young planet.
Perhaps the most important aspect of the University of Oxford team’s investigation was determining that the hydrogen present in the meteorite was there all along, not from contamination. This suggests that the material from which our planet was built was far richer in hydrogen than previously thought.
Read More: Where Did Earth’s Water Come From?
Hydrogen on the Meteorite
A previous study led by a French team had identified traces of hydrogen within both organic and inorganic components of a different meteorite. However, the remainder was unaccounted for — meaning it was unclear whether the hydrogen was native or due to terrestrial contamination.
To pinpoint hydrogen on this meteorite (named LAR 12252, originally collected from Antarctica), they blasted it with powerful X-rays from a massive machine called a synchrotron. This technique is often used to probe the chemical structure of both living and nonliving samples.
The team initially thought any hydrogen in the meteorite would be linked to sulfur molecules and aimed the beam accordingly. Much to their surprise, they found areas rich in hydrogen sulfide just outside areas they suspected would hold the most hydrogen, with the highest concentration “locked” inside a crystalline structure.
In comparison, areas of the meteorite that had cracks or rust (a sign of Earthly contamination) had little to no hydrogen present. Those two findings together create a strong argument for the hydrogen being present in the material all along — not from recent contamination.
“We were incredibly excited when the analysis told us the sample contained hydrogen sulfide — just not where we expected!” Tom Barrett, an Oxford graduate student and an author of the paper, said in a press release. “Because the likelihood of this hydrogen sulfide originating from terrestrial contamination is very low, this research provides vital evidence to support the theory that water on Earth is native — that it is a natural outcome of what our planet is made of.”
Rich in Hydrogen
Since the proto-Earth was made of material similar to enstatite chondrites, by the time the immature planet had grown large enough to be struck by asteroids, it would have already stashed enough hydrogen to explain Earth’s present-day water supply.
Although this study likely won’t resolve the debate over Earth’s original water source, it tilts the table toward an internal, not external one.
“We now think that the material that built our planet — which we can study using these rare meteorites — was far richer in hydrogen than we thought previously,” James Bryson, an Oxford professor and an author of the paper, said in a press release. “This finding supports the idea that the formation of water on Earth was a natural process, rather than a fluke of hydrated asteroids bombarding our planet after it formed.”
Read More: Earth’s Water Is Older Than the Sun
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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
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