Nitrogen fixation by volcanic lightning in the early Earth

We examine an unusual mechanism to fix nitrogen in the early Earth by lightning discharges occurring inside explosive volcanic clouds containing gases characteristic of Hawaiian volcanoes as a model of Archean volcanic volatiles. The products are predicted on thermodynamic equilibrium assumptions of the chemical species frozen out as the lightning channel rapidly expands and cools to ∼ 2400°C. Volcanic lightning is simulated in the laboratory by flowing the gas mixture into a microwave discharge cavity where the gases are excited and then the products are analyzed downstream by chemical ionization mass spectrometry. Nitric oxide was found to be the major product formed with an energy yield of ∼1 × 10 16 molecule J −1 . It is estimated that about 10 12 −10 13 g of NO could have been produced annually by volcanic clouds occurring about 4 Gyr ago.