Snowball spud gun shows comets could have seeded Earth with life

A good impact and it's a peptide hoe-down

Scientists have been speculating for years now that comets might have seeded life on Earth, but a Japanese team has performed an experiment that shows it's a valid possibility.

Dr Haruna Sugahara from the Japan Agency for Marine-Earth Science and Technology in Yokohama, and Dr Koichi Mimura from Nagoya University built makeshift comets of amino acid, water ice, and silicate and froze them down to –320.8 degrees Fahrenheit (–196 degrees Centigrade).

Then they used a projectile launcher to slam the comets into a hard surface to simulate impact and analyzed the remains. The results showed that the impact had made some of the amino acids fuse into peptides, which – given a few billion years – could have evolved into higher forms of life.

"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," said Dr Sugahara.

"Comet impacts are normally associated with mass extinction on Earth, but this work shows that they probably helped kick-start the whole process of life in the first place.

In 2004 the NASA Stardust mission successfully took a sample from the comet Wild-2 and returned it to Earth two years later. In 2009, after a lot of tests to check for human contamination, NASA confirmed that the comet did contain amino acids, specifically glycine.

This was confirmed again in 2013 when fragments of a comet that exploded over Sri Lanka were collected. Analysis of the remains found non-terrestrial life, including a complex, thick-walled microfossil similar to plankton, within the comet's remains.

This latest research shows that a cometary impact on Earth could have seeded the basic building blocks of life. That doesn't mean that's what happened in our case, but Dr Sugahara said it raises interesting possibilities for life on other planets.

"This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth. It also opens the likelihood that we will have seen similar chemical evolution in other extraterrestrial bodies, starting with cometary-derived peptides," Mimura explained.

"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."

On Tuesday the two scientists presented their findings to the Goldschmidt2015 Geochemistry Conference in Prague. ®