A Cambridge-led study has challenged the idea that comets reliably supplied the young Earth with the chemical ingredients for life. Published in Scientific Reports on October 28 and receiving fresh coverage on October 29, the research finds that delivering useful concentrations of hydrogen cyanide would have been exceptionally rare. The authors do not exclude an isolated successful impact.
According to the University of Cambridge, Richard Anslow and colleagues combined models of comet populations, atmospheric entry and impacts. Comets contain carbon- and nitrogen-bearing molecules, making them plausible chemical suppliers. The team focused on hydrogen cyanide, or HCN, a compound found in comets that can support reactions involved in producing life’s molecular building blocks.
The paper reports 100,000 simulations of Earth’s bombardment history. In 54% of these, no impact delivered the required HCN concentration onto exposed land. The median was zero even under assumptions favourable to delivery. High speeds can destroy the molecules, while passage through the atmosphere breaks up vulnerable comets. Surviving material can then become too diluted to support the chemistry being tested.
The authors also compared planets and found Mars more favourable for delivery because of lower impact speeds and its thin atmosphere. That comparison uses simplified environmental assumptions and does not establish that life arose there. For Earth, uncertainties about the ancient atmosphere and exposed land remain important; the study evaluates a particular chemical pathway rather than directly observing the origin of life.
Cambridge says alternative sources include chemistry associated with asteroid impacts or processes on Earth itself. The authors suggest that planetary systems where repeated gravitational encounters slow comets could help guide future searches for habitable worlds. Their results narrow the conditions under which cometary delivery could work, while leaving the broader question of how life began unresolved.
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