The evolution of Earth's atmosphere as recorded by continental crust

Nitrogen is the most abundant gas in today's atmosphere, but this may not always have been the case. A recent survey of different rock types suggested that large quantities of nitrogen are stored in the mantle and continental crust (Figure 1), indicating that nitrogen can transition between the atmosphere and geosphere. This is important because the mass of Earth's atmosphere, and fluctuations therein, exert a massive control on Earth's deep-time climate, and the development of habitability. The long-term evolution of the geological and atmospheric nitrogen cycle is currently unknown [2] (Figure 2). Some data suggest that atmospheric pressure was markedly lower in the Archean (2.7 billion years ago) [3], which would imply that a larger fraction of nitrogen was stored in rocks at that time. On the other hand, recent measurements of Archean crustal rocks show low nitrogen abundances [4], suggesting that nitrogen was transferred from the atmosphere into the geosphere. The most likely transfer pathway is uptake of atmospheric N2 into biomass as ammonium [5], followed by biomass burial in sediments and accretion of sediments onto continental crust. However, the efficiency of this pathway is not well constrained, and it is unknown how the sequestration of nitrogen into minerals and rocks has changed, over time [6]. In short, it is unknown where nitrogen was in the past and how it got there. This project aims to address these questions with particular emphasis on reconstructing the growth and isotopic composition of the continental nitrogen reservoir and its relationship with atmospheric N2 abundances over the course of Earth's history.