When large meteorites and comets impacted into Earth’s seas, it created structures that provided favorable conditions for life to develop, geochemists from the Trinity College Dublin School of Natural Sciences reported this week in the journal Geochimica et Cosmochimica Acta.

Once those conditions developed, interactions between water and impact-heated rock enabled the synthesis of complex organic molecules, lead author Edel O’Sullivan and her colleagues said in a statement. Ultimately, these craters evolved into self-contained habitats where life flourished, the researchers added, noting that the discovery could solve the mystery of the origins of life.

Previously, scientists have suggested that the materials left behind the meteor and comet impacts contained organic materials such as water, glycine, and β-alanine – substances which would have served as the raw materials for organisms to develop – as well as the energy needed for synthesis to occur. In the new study, however, O’Sullivan’s team proposes the hypothesis that these impact craters served as ideal environments for the first “seeds of life” to emerge.

“Previous studies investigating the origin of life have focused on synthesis in hydrothermal environments. Today these are found at mid-ocean ridges – hallmark features of plate tectonics, which likely did not exist on the early Earth,” she explained. “By contrast, the findings of this new study suggest that extensive hydrothermal systems operated in an enclosed impact crater at Sudbury, Ontario, Canada.”

A potential new pathway to explain how organisms first emerged

While no ancient terrestrial impact craters are preserved there, the authors noted that the Sudbury basin afforded them the opportunity to study sediment that would have given them a good look at what those early ecosystems might have looked like. The Sudbury location has been described as unique due to a thick basin fill and its carbon and hydrothermal metal-rich deposits.

“Due to later tectonic forces, all the rocks of the once ~200 km-wide structure are now exposed at the surface rather than being buried,” said senior author Balz Kamber, a professor of geology and mineralogy at Trinity. “This makes it possible to take a traverse from the shocked footwall through the melt sheet and then across the entire basin fill. To a geologist, this is like a time journey from the impact event through its aftermath.”

Kamber, O’Sullivan and their colleagues collected samples from throughout the basin, analyzing each for their chemical composition and carbon isotope content. Based on their work, they were able to conclude that the crater had become filled with seawater at an early stage, and that it had remained isolated from the open ocean long enough to deposit more than 1.5 km of volcanic rock and sediment.

The bottom layer was comprised of rocks that formed when water entered the crater at a time when its floor was covered by hot impact melt, the researchers explained. Coolant reactions then led to the deposition of volcanic rocks, promoting hydrothermal activity. The layer above these deposits marks the first appearance of reduced carbon, and this is where the volcanic products started to become increasingly basaltic. The data indicates that microbial life within the crater’s basin was responsible for the presence of carbon and the depletion of some nutrients.

“There is clear evidence for exhaustion of molybdenum in the water column, and this strongly indicates a closed environment, shut off from the surrounding ocean,” said O’Sullivan, adding that these isolated, submerged impact basis could represent a new explanation for how the core conditions that led to the synthesis of living organisms originally occurred.

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Image credit: Thinkstock

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