Cambridge Study Challenges Theory That Comets Delivered Life’s Ingredients
A University of Cambridge study says comet impacts were unlikely to deliver life-building molecules to early Earth intact. Computer simulations found no…
University of Cambridge researchers say a study claims long-held theory that comets delivered life-building molecules to early Earth may be wrong. Their computer simulations found that comet impacts were generally too fast to leave the fragile organic molecules intact.
The finding challenges a longstanding explanation for how the chemical ingredients of life arrived on Earth. Researchers published the study in Scientific Reports, arguing that a successful delivery by comet would have been rare and might still not have supplied molecules at a useful concentration.
“It’s kind of a romantic idea, but our results suggest it’s highly unlikely,” lead author Richard Anslow, from the University of Cambridge’s Institute of Astronomy, said in a statement.
Why do researchers doubt the comet theory?
The simulations focused on whether molecules carried by comets could survive the high-speed collision with Earth. Researchers said the impacts could generate enough heat and pressure to destroy those chemical precursors.
Comets contain carbon- and nitrogen-bearing molecules that scientists have considered potential ingredients for prebiotic chemistry: the reactions that form building blocks of life. But the researchers found that the objects’ speed and impact angle made successful delivery unlikely.
The team simulated the early planetary period 100,000 times, according to the study. In 54% of simulations, there was no impact; the other 46% included at least one collision, while a tiny minority produced up to three.
“Given what we know about surface environments on the early Earth, on average, our simulations found that there were no successful impacts,” Anslow said.
What could the finding mean for life’s origins?
The results do not rule out a comet delivering intact molecules in an unusual collision. Anslow said such an event would need the right speed and angle, followed by conditions that allowed the chemistry to continue.
“We can’t rule out confidently that there was never a successful impact — there could have been one of these fluke impacts,” he said.
Even a successful collision might not have provided enough material. The study says the molecules would need to arrive at a suitable concentration, while an impact in an ocean could cause them to dissolve quickly. Prebiotic chemistry also needs other precursor molecules, including compounds containing phosphorus and sulfur.
That distinction matters because the theory is about more than whether comets carried organic material: it asks whether they could deliver it intact and in conditions where it could contribute to the chemistry that precedes life. The simulations suggest comet impacts may not have been a dependable route for supplying those ingredients to early Earth.
Researchers point to asteroids as another possible source. They said asteroids hit Earth more frequently, though the study does not establish that they supplied the ingredients for life.
The simulations also raise a possibility about Mars. Because Mars is smaller than Earth and has a thinner atmosphere, comets may have been more likely to reach its surface during the period when such objects were more common.
“This is not to say it definitely happened on Mars, of course, but suggests it would be unlikely if it happened on Earth and didn’t happen on Mars,” Anslow said.
He also offered a more cautious alternative: “Or the other, perhaps more likely, alternative is that it didn’t happen on either planet.”
