title: The continuing puzzle of the great oxidation event.
abstract: The rise of atmospheric O(2) was a milestone in the history of life. Although O(2) itself is not a climate-active gas, its appearance would have removed a methane greenhouse present on the early Earth and potentially led to dramatic cooling. Moreover, by fundamentally altering the biogeochemical cycles of C, N, S and Fe, its rise first in the atmosphere and later in the oceans would also have had important indirect effects on Earth's climate. Here, we summarize major lines of evidence from the geological literature that pertain to when and how O(2) first appeared in significant amounts in the atmosphere. On the early Earth, atmospheric O(2) would initially have been very low, probably <10(-5) of the present atmospheric level. Around 2.45 billion years ago, atmospheric O(2) rose suddenly in what is now termed the Great Oxidation Event. While the rise of oxygen has been the subject of considerable attention by Earth scientists, several important aspects of this problem remain unresolved. Our goal in this review is to provide a short summary of the current state of the field, and make the case that future progress towards solving the riddle of oxygen will benefit greatly from the involvement of molecular biologists.
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Alex L
authors.initials: AL
authors.lastname: Sessions
authors.forename: David M
authors.initials: DM
authors.lastname: Doughty
authors.forename: Paula V
authors.initials: PV
authors.lastname: Welander
authors.forename: Roger E
authors.initials: RE
authors.lastname: Summons
authors.forename: Dianne K
authors.initials: DK
authors.lastname: Newman
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D055593:Geological Phenomena; D017752:Greenhouse Effect; D049690:History, Ancient; D008670:Metals / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis* / Q000266:history*; D010788:Photosynthesis / Q000502:physiology*; D013455:Sulfur / Q000737:chemistry
chemical_list: D008670:Metals; D013455:Sulfur; D002244:Carbon; D010100:Oxygen