Cometary impacts an unlikely pathway towards the origins of life on Earth

An early period of cometary bombardment has long been speculated to provide an important source of prebiotic feedstock molecules, required for the origins of life on Earth. In support of this interpretation, comets boast a rich diversity of volatile organic molecules, with many thought to be limiting for prebiotic chemistry. Modelling studies suggest, however, that a significant proportion of these molecules will be destroyed during hypervelocity impact. Here, we revisit the ability of comets to deliver prebiotic feedstock molecules in the high concentrations required for prebiotic chemistry, leveraging recent advances in cometary impact simulations, comet-atmosphere interactions, and dynamical modelling of short-period comets’ origin and evolution. Taken together, the rapid decline in Earth’s cometary impact bombardment and the efficient destruction of fragile cometary organics indicate that the successful delivery of prebiotic feedstock molecules was an exceedingly rare event. Our results therefore challenge the long-held assumption that cometary impacts played an important role in the origins of life on Earth.