Life on Earth needs nitrogen to survive, but little is known about how it became available to the earliest organisms. The research suggests that volcanoes may have fertilised the advent of life on the early Earth.

Although nitrogen makes up the majority of the air we breathe, our bodies are unable to absorb it in this form. Before we can access the reservoir of atmospheric nitrogen it must first be 'fixed' into forms (such as ammonia or nitrogen oxides) that can be absorbed by the plants that we, or animals lower down the food chain eat. This is called 'biologically-available' nitrogen. This is why we put nitrogen-containing fertilisers on soils to increase their fertility.

Some bacteria and fungi have evolved the ability to fix nitrogen themselves and these biological processes, along with mankind's activities (such as the burning of fossil fuels) are the major sources of fixed nitrogen in present-day ecosystems.

But the question remains as to where the fixed nitrogen came from that enabled life to evolve in the first place? Previously, lightning and asteroid impacts have been suggested as the major fixed nitrogen sources in the Earth's atmosphere of about three billion years ago; volcanism had not previously been thought of as an important process.

New work published this month shows that the high temperatures associated with volcanic activity might also have played an important role in helping to fix nitrogen. Researchers Tamsin Mather and David Pyle from the University of Cambridge's Department of Earth Sciences measured the compositions of gases above a hot lava lake at Masaya volcano in Nicaragua, and found that there were higher levels of fixed nitrogen in the volcanic plume than in the surrounding air.

This shows that the heat from the volcano allows the nitrogen and oxygen in the atmosphere to react together to form fixed nitrogen. From these measurements, the researchers were able to estimate for the first time the rate at which nitrogen could be fixed by volcanoes.

Surprisingly, the results suggest that volcanism may have been at least as important as lightning and asteroid impacts in converting atmospheric nitrogen into a bio-available form in the earliest Earth. This unexpected result asks new questions about the role of volcanism during the evolution of a habitable planet.

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