VOLCANOES could be the answer to two key mysteries about how life got started on Earth. They may have forged the form of nitrogen crucial to life, and helped produce primitive protein chains, according to two separate studies.
There was plenty of volcanic and other geothermal activity on early Earth. There is also evidence that the first life forms may have been heat-loving organisms. So researchers looking for clues to where life took hold have focused on geothermally active regions such as volcanoes and deep-sea vents.
One of the pieces of the puzzle involving the origin of life concerns nitrogen. Although the gas is abundant in the atmosphere, to be biologically useful it must be 鈥渇ixed鈥� into forms such as nitrogen oxides (NOx). 鈥淭oday organisms can [fix] nitrogen, but on the early Earth, before biological activity, another process must have been responsible,鈥� says David Pyle, a geologist at the University of Cambridge.
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Asteroid impacts and lightning were thought to be responsible for producing fixed nitrogen 3 to 4 billion years ago. But while Pyle was studying the Masaya volcano in Nicaragua he unexpectedly discovered that levels of NOx gases were 10 times higher in the volcano鈥檚 emissions than in the surrounding air. Pyle and his colleagues have worked out that volcanoes now produce NOx mainly from atmospheric nitrogen and oxygen. But their calculations show that even in the oxygen-poor environment of primitive Earth, ancient volcanoes would have been a major source of NOx, using oxygen from the carbon dioxide in the magma (Geology, vol 32, p 905).
Volcanoes could also have played a role in another important step in the evolution of life on Earth: the formation of peptides, or small proteins, from amino acids. This step has long been considered the missing link in the story of how the first proteins came about.
Now Reza Ghadiri of the Scripps Research Institute in La Jolla, California, and his colleagues have shown that when the volcanic gas carbonyl sulphide reacts directly with amino acids it encourages them to link up in chains of up to four amino acids to create peptides. And the reaction occurs under a wide variety of plausible prebiotic conditions, joining up to 80 per cent of the available amino acids into peptides (Science, vol 306, p 283). 鈥淕as that spews directly out of a volcano can do this,鈥� Ghadiri says. 鈥淵ou really can鈥檛 get a simpler process.鈥�
Ghadiri鈥檚 group now aims to test whether carbonyl sulphide can help in other biological processes, and Pyle鈥檚 team plans to study how different types of volcanic eruptions and magma flows contribute to NOx production.
鈥淭his offers an awful lot of food for thought,鈥� says George Cody, an origin-of-life researcher at the Carnegie Institution of Washington DC. He points out that volcanoes are also known to produce other interesting chemicals, such as metallic compounds that can accelerate chemical reactions. 鈥淭he lesson is that when you look around volcanoes and other similar environments you see remarkably intriguing chemical reactions,鈥� he says.