A long-standing theory says comets brought the building blocks of life to Earth, but new research challenges this idea. The study finds that such an event would have been extremely rare, calling it a “one-in-a-million occurrence.”
Scientists at the University of Cambridge found that comets heading toward Earth would have been moving too fast for delicate organic molecules to survive the impact. Their findings, published today in Scientific Reports, challenge a theory that has shaped ideas about the origins of life for almost a century. Now, the big question is: where did the ingredients for life really come from?
Why Comets Are Unlikely to Have Delivered Life’s Building Blocks
Comets have often been seen as possible carriers of prebiotic molecules because they contain carbon and nitrogen compounds linked to life’s chemistry. But computer simulations led by Dr Richard Anslow at Cambridge’s Institute of Astronomy show that the speed and angle of comet impacts make successful delivery very unlikely. The team looked at hydrogen cyanide (HCN), a molecule often found in comets that is important for prebiotic chemistry.
Their models showed that even if HCN survived the impact, it probably wouldn’t stay concentrated enough for the chemical reactions needed for life to start. “It would really have to be a one-in-a-million occurrence, because not only would you need an impact at just the right speed and just the right angle, you would also need everything to happen after that point, in terms of the concentration and the speed at which the chemical origins of life got going,” said Anslow.
Early Earth Offered Few Opportunities for Successful Comet Impacts
The researchers used new comet impact simulations, atmospheric models, and studies of the solar system’s history to see if comets could have realistically brought Earth’s early chemical ingredients. Their results show that chances were very limited, especially since comet impacts dropped off quickly during Earth’s first 500 million years.
Even in the best cases, only a few impacts might have delivered enough hydrogen cyanide. This goes against earlier ideas that repeated comet impacts steadily supplied the materials needed for life. The researchers say that while successful delivery isn’t impossible, it would have been a rare coincidence, not a regular process. In short, comets were not a reliable source of life’s ingredients.
Mars May Have Been More Favorable for Cometary Delivery
While the study casts doubt on comets bringing life’s building blocks to Earth, it suggests Mars might have had slightly better conditions. The researchers found that Mars’s smaller size and thinner atmosphere could have made it easier for comets with organic molecules to reach the surface early on. Still, the team emphasized that this doesn’t mean comets actually delivered prebiotic compounds to Mars. “This is not to say it definitely happened on Mars,” said Anslow, adding that it’s more likely successful delivery happened on neither planet.
Even so, these findings could help scientists learn more about the different chemical environments on early Earth and Mars, especially as they keep looking into whether Mars ever had conditions that could support life.
So Where Did Life’s Ingredients Come From?
If comets didn’t bring Earth’s building blocks, then what did? It’s possible that chemical reactions from asteroid impacts or natural processes on early Earth played a role. The main point is that we still don’t know the source, and this study highlights how much we have yet to learn about the chemical changes that turned a lifeless planet on a minor spiral arm in the outskirts of a galaxy into one that could support living things — like us.
Wishing you clear skies and wide eyes.