EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrogen fixation by lightning and its role for early life on Earth and exoplanets

Patrick Barth1,2,3, Eva E. Stüeken1, Christiane Helling2,3, Lukas Rossmanith1, Wendell Walters4, and Mark Claire1
Patrick Barth et al.
  • 1University of St Andrews, Centre for Exoplanet Science, St Andrews, UK (
  • 2Space Research Institute, Austrian Academy of Sciences, Graz, Austria
  • 3Technical University Graz, Faculty of Mathematics, Physics and Geodesy, Graz, Austria
  • 4Brown University, Institute at Brown for Environment and Society, Providence, RI, USA

Nitrogen is an essential building block of DNA, RNA, and proteins and, subsequently, it must have been bioavailable since the origin of life. On modern Earth, biological sources are mostly responsible for making nitrogen bioavailable via N2 fixation with only a few percent coming from abiotic sources. On early Earth, before the origin of life and the onset of biological nitrogen fixation, these abiotic sources such as lightning must have been the dominant producer of bioavailable nitrogen. Previous experiments have shown that in N2-dominated atmospheres lightning leads to the formation of nitrate (NO3-) and nitrite (NO2-), which could not only have facilitated the origin of life but also sustained the earliest ecosystems. This hypothesis has been difficult to test with the available rock record because geochemical fingerprints of this fixed nitrogen source have not been developed. We present new results from spark discharge experiments in varying atmospheric compositions corresponding to different points of time in Earth’s evolution. We find substantial amounts of nitrate are produced in an N2/CO2 atmosphere. Furthermore, we investigate the effect of lightning on the isotopic composition of the resulting nitrogen oxides in solution. Our fixed nitrogen is depleted in heavy 15N in comparison to atmospheric N2, in line with rock samples older than 3.2 billion years. For the first time we can assess to what degree lightning chemistry may have influenced the origin and early evolution of life. However, the spark in our experiment is much smaller and cooler than lightning channels in Earth’s atmosphere. To extrapolate our experimental results to full-scale planetary atmospheres we plan to complement them with simulations of the atmospheric chemistry of exoplanets and Earth. This will allow us to extend our experiments to real lightning conditions and develop observable tracers for lightning chemistry in exoplanetary atmospheres. Being able to predict the bioavailability of nitrogen on other worlds will be another factor determining the potential habitability of these worlds.

How to cite: Barth, P., Stüeken, E. E., Helling, C., Rossmanith, L., Walters, W., and Claire, M.: Nitrogen fixation by lightning and its role for early life on Earth and exoplanets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5445,, 2022.


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