Scientists said on Thursday they may have demonstrated a way that life on Earth could have been "seeded" from outer space.
They cooked chemicals commonly found in space under simulated sunlight and found that compounds important to life -- including alcohols and ethers -- formed. It's only a few steps from there to form amino acids, the basic building blocks of proteins, which make up all life.
Writing in the journal Science, Max Bernstein of the NASA-Ames Research Center in Moffett Field, California, and colleagues said they worked with polycyclic aromatic hydrocarbons, or PAH. On Earth these compounds are most commonly found in smoke and are a breakdown product when organic material is burned.
But they are also very common in space.
"It is assumed that PAH molecules are produced in the outer atmospheres of carbon stars," Pascale Ehrenfreund of the Austrian Academy of Sciences wrote in a commentary on the study.
They are often carried to Earth on meteorites, and traces were found on a Martian meteorite that scientists believe may hold evidence of early bacterial life on Mars.
Bernstein's group mixed PAHs with a little water -- considered essential for life -- and exposed them to ultraviolet rays like those coming from the sun. Before life evolved on Earth the atmosphere would have been much thinner and ultraviolet rays would have bombarded the planet.
They got a mixture of compounds.
"Some of the molecules produced here are biologically interesting and therefore might contribute to establishing the primordial boundary conditions of the origin of life," researchers wrote in the report.
Some of the compounds are the same ones that are essential to cell function, they said.
"Could these molecules hold clues for the origin of life?" Ehrenfreund asked.
Although PAHs themselves are not a key molecule for the formation of life, they are a byproduct of living material, he said. And the study indicates they could have been part of an intermediate step from nonliving material to life.
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