Local scientists have uncovered new evidence that comets or meteorites could have helped create life on Earth.

A team of chemists from the University of Hawaii at Manoa and the University of California, Berkeley, found that complex dipeptides, or linked pairs of amino acids that form proteins, enzymes and other complex molecules, could have been created on icy interstellar dust that is a precursor to comets.

“Everyone knew so far that amino acids could be produced in outer space and scientists also found them in meteorites,” said Ralf Kaiser, professor of chemistry at UH-Manoa and a coauthor of the study. Up till now, scientists had only found one kind of dipeptide in a meteorite.

That led some scientists to believe that complex dipeptides were formed after amino acids were delivered to Earth from space.

However, Kaiser said, “There has been no consensus that the amino acids, once delivered to Earth, could form dipeptides or more complex polypeptides since these amino acids are likely too diluted in the ocean. Based on our experiments, a more likely scenario is that dipeptides could have been delivered from outer space rather than being formed on Earth”

Kaiser and UH-Manoa postdoctoral fellow Seol Kim set out to see if complex dipeptides could be formed from amino acids in an environment mimicking the conditions of interstellar space.

“It has been known that amino acids can be formed by ionizing radiation, so what we were trying to do is use these simple molecules, irradiate them, and see if biologically significant molecules could be formed,” Kaiser said.

From 2011 to 2012, Kaiser and Kim simulated interstellar grains, silicate- and/or carbon-based nano particles covered with hundreds of layers of condensed molecules referred to as ice, and zapped them with high-energy electrons to simulate the ionizing radiation of cosmic rays. When zapped, chemicals, like carbon dioxide, ammonia and methane, on the grains reacted to form dipeptides.

UC-Berkeley scientists then analyzed the molecules from the cooled irradiated grains and found nine different amino acids and at least two dipeptides.

Kaiser said the findings from this study “might change the thinking that dipeptides can be directly seeded to Earth from outer space.”