Cambridge study finds comet impacts unlikely to have delivered life's building blocks to Earth

A research team led by the University of Cambridge used advanced computer models to examine whether comets could have supplied the organic compounds needed for life on early Earth. The simulations focused on hydrogen cyanide (HCN), a simple molecule commonly found on comets, and evaluated its survival during high-speed impacts.

The results indicate that the intense heat generated by comet collisions would have vaporized the majority of HCN, and any surviving amounts would have been too small to be significant. Lead author Richard Anslow said, "> It would really have to be a one-in-a-million occurrence. We can't rule out for certain that it happened that way, but it seems to be a really rare occurrence — at best, a one-off fluke."

The study also notes that only comets larger than roughly 300 feet could penetrate Earth's early atmosphere without disintegrating, and earlier estimates had overstated the amount of HCN that could survive such impacts. By contrast, asteroids, which struck Earth more frequently, may have provided the necessary chemical reactions, or the required molecules could have formed on the planet itself.

Anslow added, "> Historically, scientists thought that comets were important for the origin of life on Earth because they carried carbon and nitrogen-bearing molecules, so these giant space snowballs were almost like a get-out-of-jail-free card that brought all the molecules a planet would need to seed life. It’s kind of a romantic idea, but our results suggest it's highly unlikely."

The findings also suggest that comet delivery would have been slightly more feasible on Mars, due to its thinner atmosphere, but the overall conclusion is that comets were unlikely to have played a major role in the emergence of life on either planet.