Study casts doubt on comets as the source of life's building blocks

The idea that comets seeded Earth with the molecules of life dates back to at least 1961. New simulations by a team led by the University of Cambridge suggest fragile molecules such as hydrogen cyanide would have been destroyed on impact.

Of 100,000 simulations

46 had an impact 54 had none

In 54 per cent of 100,000 simulations of early Earth no comet struck, and in the other 46 per cent at least one did, yet on average none delivered the molecules intact.

The lead author says Mars, where comets arrive more slowly, may have been better suited. Samples from the asteroids Bennu and Ryugu contain most of the amino acids that build proteins.

The study, published in Scientific Reports, does not rule out a rare fluke. One outside scientist says comets may still have supplied other organic compounds.