How low can you go? Maximum constraints on hydrogen concentrations prior to the Great Oxidation Event

Shaw postulates that Earth’s early atmosphere was rich in reducing gases such as hydrogen, brought to Earth via impact events. This commentary seeks to place con-straints on this idea through a very brief review of existing geological and geochemical upper limits on the reducing power of Earth’s atmosphere prior to the rise of oxygen. While these constraints place tight limits on this idea for rocks younger than 3.8 Ga, few constraints exist prior to that time, due to a paucity of rocks of that age. The time prior to these constraints is also a time frame for which the proposal is most plausible, and for which it carries the greatest potential to explain other mysteries. Given this potential, several tests are suggested for the H 2 -rich early Earth hypothesis. *shawn.goldman@nasa.govDomagal-Goldman, S., 2014, How low can you go? Maximum constraints on hydrogen concentrations prior to the Great Oxidation Event, in Shaw, G.H., ed., Earth’s Early Atmosphere and Surface Environment: Geological Society of America Special Paper 504, p. 11–13, doi:10.1130/2014.2504(02). For permission to copy, contact editing@geosociety.org. © 2014 The Geological Society of America. All rights reserved.