New Research Questions Whether Comets Seeded Early Earth With Life’s Ingredients

WHO:

KSL News - Lead author Richard Anslow conducted the research while completing his doctorate at the Institute of Astronomy at the University of Cambridge in the United Kingdom.

CNN - Lead author Richard Anslow said simulations found no successful comet impacts on average, given what is known about early Earth’s surface environments.

KSL News - Queenie Chan, an associate professor of Earth sciences at Royal Holloway University of London, was not involved in the study. She said comet chemistry before atmospheric entry could have produced less volatile compounds that were more likely to survive.

CNN - Nicolle Zellner, a professor of physics at Albion College in Michigan, said she was not surprised by the findings but was reluctant to rule out comets as contributors to life’s emergence.

WHAT:

KSL News - Computer simulations challenge the theory that comets delivered life-starting organic molecules to early Earth, finding that impact speeds and resulting heat and pressure would have destroyed most fragile molecules.

CNN - The study, published in the journal *Scientific Reports*, modeled early Earth’s comet bombardment 100,000 times. Earth may have encountered more than 100,000 comets larger than 100 meters (328 feet).

KSL News - In 54% of simulations, no comet impact occurred; in the other 46%, at least one occurred, and a “tiny minority” had up to three collisions. Anslow said a successful impact could not be ruled out, but it would require a “perfect location.”

CNN - The study focused on hydrogen cyanide (HCN), detected in dozens of comets, including Halley’s and Hale-Bopp. Combined with water, HCN can contribute to amino-acid formation.

KSL News - Anslow said even a successful impact was unlikely to deliver HCN at a useful concentration; in an ocean impact, it would quickly dissolve. Comets do not routinely contain other needed precursor compounds, including phosphorus- and sulfur-containing compounds.

CNN - Alternative explanations include Earth’s primordial soup producing life’s molecular building blocks and asteroids delivering organic material. Anslow cited samples from asteroids Bennu and Ryugu, which contain most protein-building amino acids.

WHERE:

KSL News - The proposed impacts occurred on early Earth. Anslow said ancient Mars may have been more suitable for comet-delivered HCN because it is smaller and farther from the sun.

CNN - Comet 67P/Churyumov-Gerasimenko was shown emitting dust and gas in an image from January 2015.

WHEN:

KSL News - The theory that comets helped initiate life dates back to at least 1961; the broader idea of panspermia was scientifically proposed in 1908.

CNN - Early Earth’s heavy bombardment occurred over 4 billion years ago.

WHY:

KSL News - Comets may have been poor suppliers of life’s ingredients because impacts were too fast and destructive, and successful delivery required other chemicals and liquid water to be present at the impact site.

HOW:

CNN - Researchers used models of comet formation and evolution to simulate early planetary conditions. Anslow said impacts shocked comets to high temperatures and pressures, potentially destroying precursor molecules.

KSL News - Chan said reactions before comets entered Earth’s atmosphere might have transformed HCN into biologically important, less volatile compounds; she said the findings do not completely rule out a cometary contribution to Earth’s prebiotic organic inventory.

(UPDATED November 1, 2026 01:58 UTC)

Simulations suggest comet impacts likely destroyed fragile molecules needed to start life on early Earth. Successful delivery appears unlikely, though scientists say comets may still have contributed. Asteroids and Earth’s chemistry offer alternatives.