The geobiological nitrogen cycle: From microbes to the mantle.
Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time. Here, we discuss the current understanding (or lack thereof) for how the unique interaction of biological innovation, geodynamics, and mantle petrology has acted to regulate Earth's nitrogen cycle over geologic timescales. In particular, we explore how temporal variations in the external (biosphere and atmosphere) and internal (crust and mantle) nitrogen cycles could have regulated atmospheric pN2. We consider three potential scenarios for the evolution of the geobiological nitrogen cycle over Earth's history: two in which atmospheric pN2has changed unidirectionally (increased or decreased) over geologic time and one in which pN2could have taken a dramatic deflection following the Great Oxidation Event. It is impossible to discriminate between these scenarios with the currently available models and datasets. However, we are optimistic that this problem can be solved, following a sustained, open-minded, and multidisciplinary effort between surface and deep Earth communities.
School of Earth & Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews, Fife, UK.
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Zerkle
School of Earth & Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, St Andrews, Fife, UK.
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Mikhail
D001272:Atmosphere / Q000737:chemistry; D005075:Biological Evolution; D018534:Earth, Planet; D005844:Geology; D008962:Models, Theoretical; D058458:Nitrogen Cycle; D012987:Soil / Q000737:chemistry
D012987:Soil