Compelling new evidence that life is seeded by comets has emerged from experiments mimicking the bombardment of early Earth.
Scientists in Japan generated protein building blocks by recreating impacts by comets containing water, amino acids and silicate.
In the tests, a propellant gun was used to fire the frozen mixture and simulate the shock of a comet striking the Earth.
Analysis showed that some of the amino acids had linked together to form chained molecules called peptides.
Recurring lengths of peptide chains form proteins, the large, complex and bioactive molecules from which all living things are made.
Lead researcher Haruna Sugahara, from the Japan Agency for Marine-Earth Science and Technology in Yokahama, said: “Our experiment showed that the cold conditions of comets at the time of the impacts were key to this synthesis, as the type of peptide formed this way are more likely to evolve to longer peptides.
“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.”
The icy moons of Jupiter and Saturn, such as Europa and Enceladus, are likely to have undergone similar cometary bombardment, said Sugahara.
Scientists believe life could have developed in a liquid water ocean below Europa’s icy surface.
The amino acid glycine had also been detected by the American space agency Nasa’s Stardust mission, which collected dust samples from Comet 81P/Wild2.
While much of the story of life has been explained, what kicked off the first step in the chemical evolution of complex biomolecules remains a deep mystery.
Once the first short peptide chains are created, much less energy is needed to expand them further.
The experiment generated short peptides up to three units long, called tripeptides.
The findings were presented at the Godschmidt geochemistry conference held in Prague, Czech Republic.