Lightning during volcanic eruptions may have sparked life on Earth

An analysis of volcanic rocks has revealed large quantities of nitrogen compounds that were almost certainly formed by volcanic lightning. This process could have provided the nitrogen required for the first life forms to evolve and thrive.

Nitrogen is a key component of the amino acids that are strung together to make the proteins on which all life depends. While nitrogen gas is abundant, plants can’t convert it into a usable form as they can with carbon dioxide.

Instead, plants get much of their nitrogen from bacteria that are capable of “fixing” the gas by converting it into nitrogen compounds, such as nitrate. But nitrogen-fixing bacteria didn’t exist when life first evolved, says Slimane Bekki at Sorbonne University in Paris, so there must have been a non-biological source early on.

The lightning from thunderstorms is one possible origin. This produces a relatively small amount of nitrates today but might 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 have produced nitrogen compounds, including amino acids.

Now, Bekki and his colleagues have shown that another source could have been the lightning that occurs in ash clouds during some volcanic eruptions.

When they collected volcanic deposits from Peru, Turkey and Italy, the researchers were initially surprised to find large quantities of nitrates in some layers. An isotopic analysis of these nitrates showed that they were atmospheric in origin and hadn’t been emitted by the volcanoes. But Bekki says that the quantities were too large to have been created by lightning during thunderstorms. “It was the amount that was really surprising,” he says. “It is really massive.” That means the nitrates were probably generated by volcanic lightning.

“When you look at the different possibilities, the most likely was volcanic lightning,” says Bekki. “We know that you get a lot of lightning when you have a massive volcanic eruption.”

Tamsin Mather at the University of Oxford says that the team’s conclusion makes sense. “We expect volcanic eruptions like those studied in the paper to generate significant lightning, so it is quite possible that volcanic lightning might have given rise to this signal,” she says.

It has been suggested that life first evolved around volcanoes, and the team’s findings show that there could have been an abundance of nitrogen compounds in this environment, says Bekki.

The idea that volcanic lightning played a key role in the origin of life isn’t new. Jeffrey Bada at the Scripps Institution of Oceanography in California has previously shown that volcanic lightning going through volcanic gases can produce molecules such as amino acids. “This paper only reinforces what I published,” he says.