Comets may not have been the seeds of life after all

By the Editorial Team · Thursday, October 29, 2026

A new study from the University of Cambridge finds that comet impacts during Earth's early history likely delivered insufficient amounts of key organic molecules needed for life to originate. This challenges the idea that comets seeded life’s building blocks, suggesting instead that these molecules were primarily generated through processes within Earth's own atmosphere.

For over a century, scientists have considered comets as a crucial source of the organic molecules necessary for the emergence of life on Earth. However, a new study led by researchers at the University of Cambridge challenges this longstanding view, suggesting that comets were unlikely to have delivered sufficient quantities of key prebiotic chemicals to the early Earth.

The Earth’s early history was marked by frequent and intense bombardment from space debris, with more than 100,000 comets, each exceeding 100 meters in diameter, colliding with the planet during the first 500 million years after its formation. Comets are known to contain significant amounts of organic compounds, including hydrogen cyanide, a molecule believed to have played a vital role in the chemical pathways that eventually produced life’s building blocks such as sugars, fats, and nucleobases. These compounds are essential for the formation of DNA and other complex molecules.

Despite the large number of comet impacts, the study’s simulations show that the vast majority of these organic materials would have been destroyed by the intense heat generated during impact events. Dr. Richard Anslow, the lead author from Cambridge’s Institute of Astronomy, explained that while comets carried carbon and nitrogen-bearing molecules, their contribution to the early Earth’s chemistry was likely negligible. "Our results suggest it’s highly unlikely that comets delivered the molecules necessary to seed life," he said.

According to the research, comets deposited an estimated 2.63 quadrillion tonnes of material on Earth over the half-billion-year bombardment period, which, while appearing substantial, amounts to only about 0.19 percent of the mass of the world’s oceans. Even if all hydrogen cyanide contained in this material had been introduced into the oceans simultaneously, it would result in a concentration around 13,000 times lower than what is needed to facilitate the formation of vital prebiotic molecules.

The study further points out that any hydrogen cyanide landing in rare surface reservoirs such as impact craters or ancient lakes would have been too diluted to support the chemical reactions necessary for life’s emergence. Instead, researchers propose that hydrogen cyanide critical to prebiotic chemistry was more likely generated through atmospheric processes. These may have been driven by heat from asteroid impacts or other energetic events, rather than being delivered directly by cometary impacts.

Published in the journal Scientific Reports, the findings encourage a reevaluation of the sources of life’s molecular precursors, emphasizing endogenous Earth chemistry over extraterrestrial delivery by comets as the primary pathway to the origin of life.

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