Reactive ammonia in the solar protoplanetary disk and the origin of Earth’s nitrogen

Terrestrial nitrogen isotopic compositions are distinct from solar and cometary values and similar to those of primitive meteorites, suggesting that Earth’s atmospheric nitrogen originates from a primordial cosmochemical source1, 2. Prebiotic organic compounds containing nitrogen that formed in the solar protoplanetary disk, such as amino acids, may have contributed to the emergence of life on Earth3, 4. However, the original reservoirs of these volatile compounds and the processes involved in their distribution and chemical modification before accretion remain unclear. Here we report the occurrence of the mineral carlsbergite (chromium nitride) within nanocrystalline sulphide inclusions of primitive chondritic meteorites using transmission electron microscopy and secondary ion mass spectrometry. The characteristics and occurrence of carlsbergite are consistent with precipitation from a chromium-bearing metal in the presence of reactive ammonia. The carlsbergite crystals have nitrogen isotopic compositions that differ from ammonia in cometary ices, but are similar to Earth’s atmospheric nitrogen. We suggest that the reactive ammonia proposed to have initiated formation of the carlsbergite came from ices within regions of the protoplanetary disk that were affected by the distal wakes of shock waves. Our findings imply that these primordial ammonia-bearing ices were a nitrogen reservoir within the formation region of the chondritic meteorite parent bodies and could have been a source of volatiles for the early Earth.