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鈥檛 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 鈥渇ixing鈥� the gas by converting it into nitrogen compounds, such as nitrate. But nitrogen-fixing bacteria didn鈥檛 exist when life first evolved, says at Sorbonne University in Paris, so there must have been a non-biological source early on.
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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鈥檚 history. The famous Miller-Urey experiment in the 1950s demonstrated that lightning in Earth鈥檚 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鈥檛 been emitted by the volcanoes. But Bekki says that the quantities were too large to have been created by lightning during thunderstorms. 鈥淚t was the amount that was really surprising,鈥� he says. 鈥淚t is really massive.鈥� That means the nitrates were probably generated by volcanic lightning.
鈥淲hen you look at the different possibilities, the most likely was volcanic lightning,鈥� says Bekki. 鈥淲e know that you get a lot of lightning when you have a massive volcanic eruption.鈥�
at the University of Oxford says that the team鈥檚 conclusion makes sense. 鈥淲e 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,鈥� she says.
It has been suggested that life first evolved around volcanoes, and the team鈥檚 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鈥檛 new. 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. 鈥淭his paper only reinforces what I published,鈥� he says.
PNAS
