About 1.8 billion years ago, the country now known as Canada was pummeled by an enormous comet. The impact resulted in the Sudbury Basin, a crater that, according to Scientific American, measures roughly 37 miles by 18 miles.
Researchers from Trinity College Dublin’s School of Natural Sciences have used the basin as an analogue for the potential comet impacts that may have heralded primordial life on Earth. Their research was published in Geochimica et Cosmochimica Acta.
The idea that life’s ingredients were ferried to Earth on a comet isn’t new. According to NASA, Earth’s first billion years were marked by a bombardment of comets and meteors, which made the planet’s conditions unconducive for the production of life. Called the Late Heavy Bombardment, this era ended around 3.8 billion years ago. Life showed up relatively soon after that, with some of the earliest fossils dated to around 3.5 billion years ago. After the Late Heavy Bombardment, “subsequent impacts may well have delivered the water and carbon-based molecules to the Earth’s surface—thus providing the building blocks of life itself,” according to NASA.
According to Edel O’Sullivan, the study’s first author, previous investigations into life’s origins have focused on hydrothermal environments. In these areas, water met with impact-heated rock and enabled the synthesis of complex molecules, the researchers proposed.
Today, these hydrothermal vents, found underwater, form at spreading ridges and converging plate boundaries.
“The findings of this new study suggest that extensive hydrothermal systems operated” in the Sudbury Basin, said O’Sullivan in a statement.
According to the authors, the sediment available at the Sudbury Basin contains carbon and hydrothermal metal deposits, and the basin fill is close to 2.5-km thick.
“Due to late tectonic forces, all the rocks … are now exposed at the surface rather than being buried,” said Prof. Balz Kamber in a statement. “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.”
After analyzing samples, the researchers determined that the crater was filled with seawater. The area remained submarine throughout deposition, and was isolated from the open ocean long enough for 1.5 km of volcanic rock and sediment to be deposited. The lower fill is dominated by rocks that formed when the seawater initially met the hot impact melt on the floor of the crater. Above those deposits, though, reduced carbon appears and the volcanic products become more basaltic.
According to the researchers, the data shows microbial life within the basin was responsible for the carbon buildup and the depletion of nutrients, like sulfate.
“This lasted until the crater rim was breached, the influx of fresh seawater promoting renewed productivity,” the researchers wrote.
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