Comets probably didn’t seed life on Earth, new study finds
For more than a century, scientists have wondered whether life on Earth began with a delivery from space. Comets carry carbon and nitrogen, life’s raw materials, so the idea was that icy visitors dropped off the molecules life needed. A new study led by the University of Cambridge says that probably did not happen.
They tested the idea with computer simulations, running 100,000 versions of Earth’s early bombardment by comets. They tracked hydrogen cyanide, which can help build life’s building blocks — including sugars and the chemical letters of DNA — and is regularly found on comets.
The problem is speed and angle. Comets travel too fast and strike Earth’s atmosphere too steeply for their fragile cargo to survive. Most molecules would burn up on impact, or fall into the ocean, where any surviving hydrogen cyanide would be diluted beyond use. “It’s kind of a romantic idea, but our results suggest it’s highly unlikely,” said lead author Dr Richard Anslow.
In 54 percent of the simulations, no comet delivered enough hydrogen cyanide. In the other 46 percent, at least one did — but briefly, the chemical dispersing too fast for life to follow. There were at most a handful of such chances in Earth’s first 500 million years. “It would really have to be a one-in-a-million occurrence,” said Anslow — at best, a one-off fluke.
Mars looks better: smaller, with a thinner atmosphere, it would let more comets reach the surface intact — more than five times as many successful deliveries as on Earth. Venus was worst, its dense atmosphere destroying most comets outright, even ones several kilometres wide.
Why it matters
It does not solve the mystery of how life began, but it narrows the search. If comets were not the delivery service, the molecules may have arrived on asteroids, which struck Earth far more often, or formed on Earth itself. It also guides the search for life elsewhere: systems where comets can slow down by bouncing between planets may be better places to look.
What happens next
The finding rests on modelling, not direct observation of the early Earth, so it is a probability, not a proof. It could guide future searches for life beyond our Solar System, especially once successors to the James Webb Space Telescope — such as the proposed Habitable Worlds Observatory — come online.
This article is for general information and education only. It is not legal or financial advice.
Sources
- https://www.ast.cam.ac.uk/news/comets-probably-didnt-seed-life-earth-after-all-new-study-suggests (University of Cambridge, 28 October 2026)
- https://www.sciencealert.com/scientists-ran-100000-simulations-of-comets-striking-earth-the-results-are-a-surprise (ScienceAlert, 29 October 2026, updated 30 October 2026)
