New Study Suggests Comets Didn't Bring Life To Early Earth After All

For more than a hundred years, scientists believed that comets crashing into early Earth delivered the chemical building blocks necessary for the origin of life. However, a new study is challenging this theory. Researchers at the University of Cambridge probed whether icy comets packed with carbon could actually transport fragile organic molecules safely onto a young planet. Their findings, published in the journal Scientific Reports, suggest they could not.

"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," lead author Dr Richard Anslow from Cambridge's Institute of Astronomy said in a statement. "It's kind of a romantic idea, but our results suggest it's highly unlikely."

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According to the study, the extreme heat and pressure generated when a comet strikes a planet would instantly destroy the delicate molecules required for life.

Rather than a steady rain of life-giving ingredients from space, scientists now believe that any successful delivery would have been a rare, "one-off fluke".

"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.

"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."

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With the comet theory heavily challenged, scientists are now looking closer to home. Experts suggest that the essential ingredients for life may have formed right here on Earth, or perhaps arrived via asteroid impacts, which were far more frequent and less destructive than comet crashes.

The team also looked at Mars and concluded that similar impacts would have likely failed there, too.

"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.

"Or the other, perhaps more likely, alternative is that it didn't happen on either planet."