A century-old theory that comets brought the building blocks of life to Earth may be completely wrong, according to a groundbreaking study.
Scientists have long believed that comets — giant icy space rocks packed with carbon- and nitrogen-bearing molecules — delivered a steady rain of prebiotics needed to seed life on Earth.
But researchers at the University of Cambridge found that the chances of those life-building prebiotic molecules surviving a comet’s high-speed impact with Earth are actually slim, according to the study published in Scientific Reports last week.
“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,” Anslow said.
Comets typically travel too fast and strike at too sharp an angle, causing the molecules to vaporize, researchers said.
But even if some building blocks survived in a “one-off fluke,” there may not be a concentration high enough to create life.
“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.”
Researchers said the molecular seeds of life could have come from several other places, such as asteroids, which hit Earth far more frequently.
Although cometary delivery of life-building molecules on Earth seems unlikely, scientists found that our neighbors in the solar system may be more habitable.
Comets would be more likely to make it on the surface of Mars, which is smaller than Earth and has a thinner atmosphere, especially during the period of the solar system’s development when the space rocks 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.
“Or the other, perhaps more likely, alternative is that it didn’t happen on either planet.”
