Comet craters helped create 'seeds of life' on Earth

Large meteorite and comet impacts into the sea may have formed the nurseries from which life on Earth first sparked, a new study has found.

Researchers from the Trinity College Dublin propose that meteorite and comet impacts created structures that provided conditions favourable for life. Water then interacted with impact-heated rock to enable synthesis of complex organic molecules, and the enclosed crater itself was a micro-habitat within which life could flourish.  It has long been suggested that the meteoritic and cometary material that bombarded the early Earth delivered the raw materials - complex organic molecules, such as glycine, beta-alanine, gamma-amino-n-butyric acid, and water - and the energy that was required for synthesis. "Previous studies investigating the origin of life have focused on synthesis in hydrothermal environments," said Edel O'Sullivan, postgraduate researcher at Trinity College Dublin. "Today these are found at mid-ocean ridges - hallmark features of plate tectonics, which likely did not exist on the early Earth," said O'Sullivan.  "By contrast, the findings of this new study suggest that extensive hydrothermal systems operated in an enclosed impact crater at Sudbury, Ontario, Canada," she said. Although no very ancient terrestrial impact structures are preserved, the Sudbury basin provides a unique opportunity to study the sediment that filled the basin as a guide to what the earlier impact craters would have looked like.  The Sudbury has an unusually thick (nearly 2.5 km) basin fill, and much of this is almost black in colour (due to carbon) containing also hydrothermal metal deposits. Representative samples across the basin fill were analysed for their chemistry and for carbon isotopes.  Researchers found that the crater was filled with seawater at an early stage, and remained sub-marine throughout deposition. The water in the basin was isolated from the open ocean for long enough to deposit more than 1.5 km of volcanic rock and sediment.  The lower fill is made up of rocks that formed when the water entered the crater whose floor was covered by hot impact melt. Fuel-coolant reactions deposited volcanic rocks and promoted hydrothermal activity. Above these deposits, reduced carbon starts and the volcanic products become more basaltic. Microbial life within the crater basin was responsible for the build-up of carbon and also for the depletion in vital nutrients, such as sulphate, researchers said. Only after the crater walls collapsed, did the study show replenishment of nutrients from the surrounding sea.  These sub-marine, isolated impact basins, which experienced basaltic volcanism and were equipped with their own hydrothermal systems, thus present a new pathway to synthesis and concentration of the stepping stones to life.