Author name: Marilyn L. Fogel

Nitrogen is a critical element for living organisms on Earth. While atmospheric N2 is plentiful, organisms find it difficult to metabolize, requiring chemical modifications that are rare or absent in abiotic chemistry. Living organisms reduce N2 to NH3 with elaborate, energy-intensive, biochemical processing to create nitrogen-bearing carbon compounds essential for life. Astrobiologists have long discussed what role nitrogen could play in shaping life on other planets. Work on Martian meteorites has provided new insights into nitrogen cycling on Mars. Research on meteorites ties into investigations by NASA’s Mars Science Laboratory that are providing on-theground information to piece together a more cohesive picture of the importance of nitrogen for establishing a habitable environment.

Nitrogen exhibits an intriguing combination of highly volatile behavior (particularly as N2), appreciable reactivity, and surprising compatibility in the deep Earth. Nitrogen is incorporated into the biosphere and then, through diagenesis and low-grade metamorphism, is conveyed into the lithosphere and the deeper Earth. The investigation of N behavior in the biosphere, hydrosphere, and atmosphere has led to many important discoveries regarding biogeochemical pathways, including in areas such as trophic interactions and anthropogenic impacts on terrestrial and marine environments (e.g. nutrient pollution, eutrophication). Nitrogen can act as an excellent tracer of the transfer of sedimentary/organic materials into and within deep-Earth reservoirs and shows great potential as a tracer of life on early Earth and elsewhere in the Solar System.