The origin of life on our planet may not be connected to comets after all, as new research questions this long-standing theory about how chemical precursors of life could have found their way to Earth.
In a recent paper published in Scientific Reports, University of Cambridge researchers claim that comet strikes would be far more likely to destroy any building blocks of life they may be carrying than to seed them on a planet like ours.
Researchers have long sought a final solution to the origin of life as we know it, with ideas ranging from a primordial soup occurring naturally on our planet to panspermia, the idea that life was seeded from elsewhere in the universe.
While the new work appears to rule out comets as the carrier of what would eventually become life on Earth, it still leaves open other possibilities for elements crucial to life arriving from space.
Comets and the Origin of Life
Some theorists have suspected that comets may have brought important building blocks for life to Earth, but the Cambridge team suggests that would have been a “one-off fluke” at best. The researchers used computer models to study the arrival of comets through Earth’s atmosphere and onto the surface.
Their work found that the journey would be much more treacherous than previous work had recognized. Organic molecules are fragile and would likely vaporize on impact because of the speed and angle at which comets would likely arrive. Their work found that Mars offered slightly better conditions for a comet-borne panspermia scenario, but enough organic molecules arriving intact was still a stretch.
“Historically, scientists thought that comets were important for the origin of life on Earth, because they carried carbon- and nitrogen-bearing molecules, so these giant space snowballs were almost like a ‘get out of jail free card’ that brought all the molecules a planet would need to seed life,” said lead author Dr. Richard Anslow from Cambridge’s Institute of Astronomy. “It’s kind of a romantic idea, but our results suggest it’s highly unlikely.”
Ping Pong Comets
In a 2023 paper, some team members proposed a theory that comets could bounce back and forth between nearby planets, reducing the high speeds they gain on their cosmic journeys. Under such a scenario, the team hypothesized that the comets may have shed organic molecules during their journeys. However, their new research modeling comet behavior demonstrated that while such a scenario is possible, it is highly unlikely.
As computer modeling has improved, scientists have refined their simulations for comet impacts, comet-atmosphere interactions, and comet evolution. These new models provided the team with an advanced set of working tools.
“We’re learning more and more all the time about how our Solar System and the Earth formed, and pulling this together with lots of different advances in modeling, which allowed us to investigate this idea that has been around for close to a century,” Anslow said.
Could Organic Molecules Survive?
Using these tools, the researchers monitored the survivability of hydrogen cyanide, an important prebiotic molecule that is commonly found on comets in our solar system. They found that the molecule rarely survived these impacts, and even when it did, it was in far too low a concentration to be useful in the propagation of life.
Comparing this low survivability with the rapid decline in comet impacts during the first half-billion years of our planet’s existence, the team found very few opportunities for successful seeding. Beyond that, even if the molecule survived to the surface, the organic chemistry required for life to arise would have had to occur incredibly quickly before the concentration became too diluted.
Cometary Conclusions
While the simulation still presents that such an event is technically possible, the researchers now believe it would have been exceedingly unlikely.
“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,” Anslow said. “We can’t rule out for certain that it happened that way. But it seems to be a really rare occurrence – at best, a one-off fluke.”
This doesn’t rule out life owing a debt to space, though. While chemical processes on Earth may have produced life without any help, the period would have seen many asteroid impacts that brought important building blocks with them.
While the bouncing comet theory appears unlikely to have produced life on Earth or Mars, the team says that future attempts to seek extraterrestrial life could consider other planetary systems where such a scenario would be more likely to occur.
The paper, “Cometary Impacts an Unlikely Pathway Towards the Origins of Life on Earth,” appeared in Scientific Reports on October 28, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.