Simulations suggest comet delivery of prebiotic chemicals to early Earth was extremely rare
Computer models of 100,000 comet impacts indicate that delivering enough hydrogen cyanide to support the origin of life on Earth would have been highly unlikely, while Mars may have been more favorable for such deliveries.
A study published in Scientific Reports used 100,000 computer simulations to assess whether comets could have supplied prebiotic chemicals to the early Earth. The researchers focused on hydrogen cyanide, a molecule detected in comets and considered a key feedstock for synthesising basic biological building blocks.
The models showed that in 54 % of runs no comet impact delivered a sufficient amount of hydrogen cyanide to land, as most comets disintegrated in the atmosphere or struck the oceans, diluting any surviving material. In the remaining 46 % of simulations, at least one impact could have deposited enough of the molecule, but the opportunity for subsequent chemistry would have been brief.
"It would really have to be a one-in-a-million occurrence, because not only would you need an impact at just the right speed and just the right angle, you would also need everything to happen after that point, in terms of the concentration and the speed at which the chemical origins of life got going," said astronomer Richard Anslow of the University of Cambridge.
The authors caution that simulations do not prove the scenario impossible, but they suggest that cometary delivery of prebiotic material to Earth was far less probable than previously thought. By contrast, the same analysis indicated that Mars, with its thinner atmosphere and lower impact velocities, could have experienced over five times more successful deliveries, while Venus’s dense atmosphere would likely have destroyed most incoming comets.
The findings add nuance to the long-standing hypothesis that life’s building blocks arrived from space, highlighting the importance of planetary conditions in assessing the plausibility of such mechanisms.