Did life on Earth come from comets?

The mere mention of comets crashing into the Earth is likely to bring to mind images of mass extinction and the end of days. But researchers at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) have found further evidence that comet impact may have been vital for the creation of life as we know it.

The team ran a series of experiments aimed at mimicking the kind of comet impacts that are likely to have occurred on Earth at the time when life first appeared, around four billion years ago. They made a mixture of amino acids (the so-called ‘building blocks’ of life), ice and forsterite, a mineral often found in meteorites. They then cooled it to 77°K and bombarded it with a propellant gun, to simulate the force of a comet impact.

Analysis of the resulting mixture showed that a number of the amino acids had joined together into short chains called peptides. “This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth,” said Haruna Sugahara, who was leadauthor of the study.

“The production of short peptides is a 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.” The work also suggests that the same process could have  occurred on other planets and other extraterrestrial bodies. 

“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. The NASA stardust mission has shown the presence of the amino acid glycine in comets,” Sugahara added.