Analysis of the volcanic rocks revealed large amounts of nitrogen compounds that were almost certainly produced by volcanic lightning. This process could provide the nitrogen necessary for the development and flourishing of early life forms.
Nitrogen is a key component of amino acids, which form the proteins on which all life depends. Although nitrogen gas is abundant, plants cannot convert it into a usable form the way carbon dioxide can.
Instead, plants get most of their nitrogen from bacteria, which can “fix” the gas and convert it into nitrogen compounds such as nitrate. However, nitrogen-fixing bacteria didn’t exist when life began, says Slimane Becky of Sorbonne University in Paris, so a non-biological source must have existed early on.
Lightning from a thunderstorm is a possible source. This produces relatively little nitrate today, but it may have been important early in Earth’s history. The famous Miller-Urey experiment of the 1950s showed that lightning in Earth’s early atmosphere could produce nitrogen compounds, including amino acids.
Now Becky and his colleagues have shown that another source could be lightning that occurs in ash clouds during certain volcanic eruptions.
When they collected volcanic sediments from Peru, Turkey and Italy, the researchers were initially surprised to find large amounts of nitrate in some layers.
Isotope analysis of these nitrates has shown that they are of atmospheric origin and are not emitted by volcanoes. But Becky says the quantities were too large to have been produced by lightning during a thunderstorm.
“The amount was really astonishing,” he says. “It’s really huge.” This means the nitrates were likely formed by volcanic lightning.
“If you look at the different options, the most likely is volcanic lightning,” says Becky. “We know that during a major volcanic eruption there is a lot of lightning.”
Tamsin Mather of the University of Oxford says the team’s findings make sense. “We expect volcanic eruptions such as those studied in the paper to produce significant lightning, so it is possible that volcanic eruptions are responsible for this signal.”
It has been suggested that life first emerged around volcanoes, and the team’s findings suggest that nitrogen compounds may be abundant in these environments, Becky says.
It’s worth noting that the idea that volcanic lightning played a key role in the origins of life is not new. Jeffrey Bada of the Scripps Institution of Oceanography in California previously showed that volcanic lightning passing through volcanic gases can produce molecules such as amino acids.
