BioEd Online

Gas belched out from prehistoric volcanoes could have helped the first life to flourish, say chemists. They have worked out that carbonyl sulphide (COS) may have been instrumental in stringing together the first molecular building blocks of biology.

The discovery potentially answers one of the most vexing questions surrounding the origins of life: just how did the first complex biological molecules appear, given that there were no organisms around to produce them?

Volcanic gas may have been responsible for creating the first rudimentary proteins, suggest Reza Ghadiri, of the Scripps Research Institute in La Jolla, California, and his colleagues. In the lab, COS can link amino acids into strings called peptides, the strands from which proteins are woven.

Ghadiri's team exposed amino acids to COS at room temperature. The researchers report in this week's Science¹ that peptide chains were produced in a matter of hours or even minutes. What's more, chains could be created through several different chemical processes, such as oxidation, alkylation and metal catalysis.

Keep it simple

"This is very simple and efficient chemistry," Ghadiri says. "The reaction rates are rapid and can proceed through multiple pathways." If similar processes occurred on the early Earth, they might have got life started towards more complex biochemistry.

And COS may have been in ready supply in life's earliest days, the researchers suggest. Today, it makes up around 0.1% of the gas spewed out by volcanoes. "It is not clear what the concentration of COS might have been in the prebiotic atmosphere, but it was probably significant," Ghadiri says.

This means that the regions around volcanoes could have been cradles for life, Ghadiri suggests. "The reaction would have occurred near the gas emission, such as in lakes by volcanoes or in areas of underwater volcanic-gas emission such as deep vents."

The theory is by no means proven. After all, we don't know for sure how much COS was around more than 3 billion years ago, when life is thought to have put in its first appearance. But the study shows that COS fits the bill as a chemical agent capable of stringing together amino acids.

We also don't know, of course, how the amino acids got here in the first place. Experts are currently divided on whether they arose on Earth, or parachuted in from elsewhere. "Amino acids could have been formed on Earth under different, plausible prebiotic conditions," says Ghadiri. "But they have also been found in meteorites, so they could have been brought to Earth as well."