Every protein molecule in every cell in your body contains nitrogen, but the abundant N2 molecules in the atmosphere are useless to you. The triple bonds that hold them together are just too strong. Atmospheric nitrogen is made available to organisms by breaking apart that N2 and bonding the free nitrogen with oxygen or hydrogen—a process known as fixation. Nitrogen fixing can be accomplished in a few ways, including biotic processing by bacteria and algae, high-energy industrial-fertilizer production, and lightning strikes.
Without fertilizer factories, algae, or bacteria around to provide the fixed nitrogen for life on Earth, its emergence would have required abiotic nitrogen fixation. Lightning has been the leading candidate for the source of that process. Lab experiments and theoretical models have suggested that volcanic lightning in particular could have played a vital role because ash and gas plumes promote the highest rates of lightning strike. Yet, until now, no significant quantities of abiotically fixed nitrogen have been found in the geologic record or from present-day eruptions.
Adeline Aroskay and Erwan Martin of Sorbonne University and their colleagues were looking in volcanic deposits for sulfates, which contribute to eruption-related climate change. They turned to rocks in arid environments in Turkey and Peru, where the soluble sulfate molecules would be preserved and not flushed away by water over time. Alongside the sulfur and chlorine compounds that they expected to find, they discovered a surprisingly high concentration of nitrates, a fixed form of nitrogen.
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