A gigantic pool of magma emerged beneath Earth’s surface following the impact event that wiped out all non-avian dinosaurs. New research suggests this hellish subterranean chamber hosted a biological ecosystem, a finding that could give clues as to how life emerged during Earth’s tumultuous early days.
When the asteroid struck our unfortunate planet some 66 million years ago, it created a 177 km-wide impact crater in what is now the Yucatan Peninsula. Evidence presented earlier this year showed the impact also produced a gigantic subterranean magma chamber, which persisted for hundreds of thousands of years, possibly even millions of years. Incredibly, this hydrothermal system supported an entire microbial ecosystem, according to new research published today in Astrobiology.
David Kring, the lead author of both studies and a geologist at the Lunar and Planetary Institute (LPI), believes the Chicxulub hydrothermal system is a possible glimpse into the early conditions on Earth, when life was starting to emerge. Kring’s co-authors are Martin Whitehouse from the Swedish Museum of Natural History and Martin Schmieder from Neu-Ulm University in Germany.
During its peak, the Chicxulub magma chamber was around 3 km thick and encompassed 140,000 cubic kilometres of Earth’s crust. By comparison, the caldera at Yellowstone National Park is nine times smaller.
Kring and his colleagues discovered evidence of this hydrothermal system in a rock core pulled from the crater’s peak ring, which is basically the jagged ring found inside some impact craters (good examples here). Approximately 15,000 kg of rock was pulled from a depth of 1.3 km, in an expedition supported by the International Continental Scientific Drilling Program and the International Ocean Discovery Program.
Delving once again into the Chicxulub sample material, the scientists spotted tiny spheres of pyrite, called framboids. Sulphur isotope analysis of these fromboids, which measure just 10 millionths of a metre in diameter, pointed to the presence of “thermophilic colonies of sulfate-reducing organisms,” in other words, clumps of heat-loving microscopic organisms with an appetite for sulfates. These microorganisms lived in the “porous, permeable rock beneath the floor of the crater and fed on sulfate transported through the rock,” which was made available by the impact-generated hydrothermal system, according to the study.
As the authors point out, these subterranean microbes made a living by taking advantage of chemical reactions happening inside the hydrothermal system, namely inside mineral-rich waters warmed by the magma. During this process, sulphate converted into sulfide, which was preserved as pyrite. These organisms are not unlike some heat-loving bacteria and archaea found at Yellowstone today.
This finding is super interesting in its own right, but it potentially speaks to the conditions found on early Earth, specifically during the Late Heavy Bombardment (LHB) period, which ended some 3.8 billion years ago. During this time, known as the Hadean period, Earth was being pummelled on a regular basis by large asteroids. The surface would’ve been a total mess and very likely uninhabitable. Yet, some of the earliest forms of life on Earth date back to around 3.5 billion years ago, and possibly around 3.77 billion years ago.
Equipped with the new evidence, Kring and colleagues speculate that the conditions beneath Chicxulub crater may have resembled conditions found during the LHB, and similar extremophiles may have eked out an existence during this early time. What’s more, prior evidence suggests the “earliest organisms on Earth were thermophilic [heat-loving] and hyperthermophilic [really, really heat loving],” so seems “plausible” that “life originated in an impact crater,” as the authors wrote in an accompanying two-page summary explaining the “impact origin of life hypothesis,” as it’s known.
OK, fantastic stuff, but let’s take a deep breath and consider some important caveats. The apparent remnants of life seen in the Chicxulub samples may not actually be life. Other scientists may take a look at the same samples and see purely abiotic processes at play, which often happens when claims like this are made. Also, environmental conditions during the Late Cretaceous were vastly different than those of the Hadean (the planet was already teeming with life, for example), so the Chicxulub hydrothermal system may not serve as a good analogue for early Earth.
More work needs to be done to bolster the impact origin hypothesis, including more fossil evidence and a fundamental understanding of the chemical processes that give rise to self-replicating molecules, namely RNA and DNA. Still, we can marvel at the possibility that our earliest ancestors emerged in fiery subterranean cauldrons churned by asteroid impacts.
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