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 needed for early life forms to develop and thrive.
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 are able to “fix” the gas, converting it into nitrogen compounds such as nitrate. However, nitrogen-fixing bacteria did not exist when life began, says Slimane Becky of the Sorbonne University in Paris, so a non-biological source must have existed early on.
Lightning from a thunderstorm is one possible source. This produces relatively little nitrate today, but it may have been important early in Earth’s history. The famous Miller-Urey experiment in the 1950s demonstrated 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 some 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.
Isotopic analysis of these nitrates showed that they are of atmospheric origin and are not emitted by volcanoes. But Becky says the amounts were too large to have been produced by lightning during a thunderstorm.
“The amount was really amazing,” he says. “It’s really huge.” This means that the nitrates were likely formed by volcanic lightning.
“If you look at the different options, the most likely would be volcanic lightning,” says Becky . “We know that during a large volcanic eruption there is a lot of lightning.”
Tamsin Mather of Oxford University says the team’s findings make sense. “We expect volcanic eruptions like those studied in the paper to generate significant lightning, so it is possible that volcanic lightning could be responsible for this signal.”
It has been suggested that life first arose around volcanoes, and the team’s findings suggest that nitrogen compounds may have been abundant in these environments, Becky says.
It’s worth noting that the idea that volcanic lightning played a key role in the emergence 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.