French geologists analyzed the composition of nitrates in Neogene volcanic deposits and found that lightning occurring in ash clouds could fix atmospheric nitrogen. The researchers found several evidence indicating that nitrates in the sediments were formed from atmospheric nitrogen.
The formation of proteins and nucleic acids is the most important process in the origin of life. But it is impossible without nitrogen, one of the most common elements on Earth. Nitrogen occupies almost three-quarters of the volume of atmospheric air, but is in a form that living organisms cannot absorb. The conversion of nitrogen into a bioavailable form is called nitrogen fixation. Now microorganisms or nitrogen fertilizers do this, but before the emergence of life, several phenomena hypothetically played the role of nitrogen fixer, including thunderstorms and volcanic lightning.
The possibility of such nitrogen fixation was proven in laboratory experiments. During eruptions, large amounts of sulfur and halogens (chlorine, fluorine, etc.) are released into the atmosphere, and lightning occurs in the ash clouds – the so-called dirty thunderstorm. During discharges, nitrogen in the air is oxidized, and the resulting oxides fall to the ground along with volcanic emissions. The resulting nitrates, fixed nitrogen, would remain in the soil. However, geological evidence of this has not yet been found.
A group of French geologists decided to find nitrate deposits in volcanic deposits after major Neogene eruptions (1.65-23.5 million years ago) in arid regions. The researchers collected samples of volcanic tephra and pyroclastic flows in Peru and Turkey and found large amounts of nitrates in these sediments along with sulfides and chlorine, indicating their volcanic origin.