Did comets spark life on Earth?

The extreme conditions may have also help kickstart life on other worlds

Comets have long been suggested as a method of bringing the basic building blocks of life to Earth
Credit: Dr Yoshihiro Furukawa

Comets have long been thought omens of bad fortune, and in the history of our planet this hasn’t proved far wrong. The chaos following both cometary and meteorite impacts has been blamed for several great extinction event, wiping out nearly all life on the planet. But could these harbingers of doom also have been responsible for creating life on Earth in the first place?

It’s been known for a long time that comets contain complex molecules, such as amino acid, that might one day go on to form life. NASA’s Stardust mission, which returned a sample of a comet’s coma to Earth, detected them, as has the Rosetta mission. What has been unclear is how these formed into the more complex peptide chains that are needed to form proteins.

It seems the impact may be the key. When an object strikes the Earth, its components are subjected to a sudden rise in temperature and pressure. Under these extreme conditions the ices and minerals that make up the object can change and form new compounds, some of which might be needed to start life.

To recreate the conditions, researchers in Japan took a mixture of amino acid, water ice and silicate (forsterite) and cooled them to 77K with liquid nitrogen to simulate a comet. The concoction was then fired from a propellant gun to simulate the impact of it striking the Earth. Analysing the resulting mixture showed that the amino acids had formed into short peptide chains.

“This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth,” says Haruna Sugahara from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in Yokahama. “The production of short peptides is the key step in the chemical evolution of complex molecules. Once the process is kick-started, then much less energy is needed to make longer chain peptides in a terrestrial, aquatic environment.”

If comets are needed to kickstart life, this could have interesting connotations for finding life elsewhere as the Earth is not the only planet to be struck by comets.

“Within our own Solar System the icy satellites of Jupiter and Saturn, such as Europa and Enceladus are likely to have undergone a similar comet bombardment,” says Sugahara. 


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