The chemical building blocks that gave rise to life on Earth probably didn’t come from comets.

Most comets would have been traveling too fast and at too steep an angle to Earth for prebiotic compounds to survive impact with the planet, researchers contend October 28 in Scientific Reports . While the study doesn’t completely rule out the possibility that comets brought these molecules to Earth, it contradicts the long-standing idea that comets seeded Earth with the chemicals necessary for life to arise.

“Even though we see that comets contain all of these molecules in really high concentrations, it’s not straightforward to go from there to saying we’re going to have all of these available for prebiotic chemistry on the surface of the Earth,” says Richard Anslow, a planetary scientist at the Met Office, the national meteorological service for the United Kingdom in Exeter.

Comets carry carbon- and nitrogen-containing molecules left over from early in the solar system’s formation.…