Computer simulations question comets' role in delivering life's building blocks to early Earth
New computer models suggest that comet impacts were unlikely to have deposited intact organic molecules on the early Earth, challenging a long-standing hypothesis about the origin of life.
Computer simulations published in Scientific Reports indicate that comet impacts during Earth's early heavy-bombardment period were generally too energetic to preserve fragile organic molecules such as hydrogen cyanide (HCN). Lead author Richard Anslow, a doctoral researcher at the University of Cambridge's Institute of Astronomy, said the models, which ran 100,000 scenarios, found no successful impacts in 54 % of cases and only a few low-probability collisions in the remainder. He added that even the rare impacts would have required a precise combination of liquid water and other chemicals to be relevant for prebiotic chemistry.
The study focused on HCN, a molecule detected in many comets and known to form amino acids when combined with water. Anslow explained that the high temperatures and pressures generated by impact would likely destroy such precursor molecules, and that comets do not consistently carry other essential elements like phosphorus and sulfur.
Alternative sources for prebiotic compounds were discussed, including synthesis in Earth's primordial environment and delivery by slower-moving asteroids, which have been shown to contain a range of amino acids in samples from Bennu and Ryugu. Anslow also noted that lower impact velocities on Mars might have allowed more HCN to survive, offering a possible avenue for future research on Martian habitability.
Commenting on the findings, Queenie Chan, an associate professor of Earth sciences at Royal Holloway University of London, said that chemical reactions occurring before atmospheric entry could still produce less volatile, biologically important compounds, meaning comets might have contributed to Earth's organic inventory in ways not ruled out by the new models. Nicolle Zellner, a physics professor at Albion College, described the results as unsurprising but emphasized that the study provides valuable constraints on the likelihood of comet-based delivery of life's precursors.