Volcanic eruptions may have sparked life on Earth through lightning

Analysis of volcanic rocks revealed large amounts of nitrogen compounds, almost certainly formed by volcanic lightning. This process may have provided the nitrogen that the first life forms needed to evolve and thrive.

Nitrogen is a key component of the amino acids that are linked to make the proteins on which all life depends. Nitrogen gas is abundant, but plants cannot convert it into usable forms like carbon dioxide.

Instead, plants get most of their nitrogen from bacteria that can “fix” the gas by converting it into nitrogen compounds such as nitrate.But nitrogen-fixing bacteria didn't exist when life first evolved. Suliman Becchi There must have been non-biological sources early on, as it was at the Sorbonne University in Paris.

Lightning from thunderstorms is one possible cause. Currently, this produces relatively small amounts of nitrate, but it may have been important early in Earth's history. The famous Miller-Urey experiment of the 1950s demonstrated that nitrogen compounds containing amino acids could have been produced by lightning in Earth's early atmosphere.

Now Becchi and his colleagues show that another source may be lightning that occurs in ash clouds during volcanic eruptions.

When researchers collected volcanic deposits from Peru, Turkey, and Italy, they were initially surprised to find large amounts of nitrate in some layers. Isotopic analysis of these nitrates showed that they were originally present in the atmosphere and were not emitted by volcanoes. But Becchi says that amount is too much to be produced by lightning during thunderstorms. “It was an amazing amount of money,” he says. “It's really huge.” That means the nitrate was probably produced by volcanic lightning.

“When we looked at the various possibilities, volcanic lightning was the most likely,” Becchi said. “We know that when large-scale volcanic eruptions occur, a lot of lightning occurs.”

Tamsin Mather Researchers at the University of Oxford say their team's conclusions make sense. “Volcanic eruptions like the one studied in the paper would be expected to produce significant lightning, so it's quite possible that volcanic lightning generated this signal,” she says.

Life is thought to have first evolved around volcanoes, and the team's findings indicate that this environment may have been rich in nitrogen compounds, Becchi said.

The idea that volcanic lightning played an important role in the origin of life is not new. Jeffrey Bada Researchers at the Scripps Institution of Oceanography in California have previously shown that volcanic lightning passing through volcanic gases can produce molecules such as amino acids. “This paper just reinforces what I've published,” he says.