Analysis of volcanic rocks has revealed a large number of nitrogen compounds, almost certainly formed by volcanic lightning. This process may have provided the nitrogen needed for the first life forms to evolve and thrive.
Nitrogen is a key component of amino acids, which are strung together to form proteins on which all life depends. Although nitrogen is abundant, plants cannot convert it into a usable form like carbon dioxide can.
Instead, plants get most of their nitrogen from bacteria, which are able to "fix" gases by converting them into nitrogen compounds, such as nitrates. But when life first evolved, nitrogen-fixing bacteria didn't exist, says Slimane Bekki of the Sorbonne in Paris, so there must have been an abiotic early life**.
Lightning from thunderstorms is a possible origin. This produced a relatively small amount of nitrate today, but could have been significant early in Earth's history. The famous Miller-Yuri experiment of the 1950s showed that lightning in the Earth's early atmosphere may have produced nitrogen compounds, including amino acids.
Now, Bekki and his colleagues have proven that another possibility is 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 nitrates in some formations. Isotopic analysis of these nitrates has shown that they originate in the atmosphere and are not emitted by volcanoes. But Becky said the numbers were too large to be caused by lightning during a thunderstorm. "This amount is really surprising," he said. "It's really big. "This means that nitrates may have been produced by volcanic lightning.
When you see different possibilities, the most likely is volcanic lightning," said Bekki. "We know that when you have a massive volcanic eruption, you get a lot of lightning.
Tamsin Mather of the University of Oxford said the team's conclusions were plausible. "We expect volcanic eruptions like the one studied in ** to produce a lot of lightning, so it's likely that volcanic lightning has already produced this signal," she said.
Evolution is Evolving: 13 Ways We Must Rethink the Theory of Nature.
It has been suggested that life first evolved around volcanoes, and the team's findings suggest that there may be abundant nitrogen compounds in this environment, Bekki said.
The idea that volcanic lightning plays a key role in the origin of life is not new. Jeffrey Bada of the Scripps Oceanographic Institution in California has previously shown that volcanic lightning passing through volcanic gas can produce molecules such as amino acids. "This article just reinforces what I've published," he said.