User:Natural ironist/sandbox

This is a draft version of revisions for Geological history of oxygen.

=Early Earth= It is generally thought that the early Earth lacked free oxygen in the atmosphere. Although oxygen is the most abundant element on earth, the majority of this is in the form of chemically inert silicate minerals, which cannot produce gaseous oxygen. [citation]

The exact atmospheric composition of the early earth is still debated. Before the origin of life, the composition of the atmosphere was dominated by volcanic gases and gases introduced by meteors during the Late Heavy Bombardment. Many older models assumed that the earth around 3.8 billion years ago had a very reduced atmosphere consisting of mainly methane, ammonia, and hydrogen gas (H2). However, if the composition of volcanic gases was similar to those observed on modern Earth, it is more likely that the atmosphere at this time mainly consisted of carbon dioxide and nitrogen gas.

Neverless, there are multiple lines of geologic evidence for an oxygen-free atmosphere in the early Archean. Pyrite and uraninite grains that show display subaerial erosion have been found from strata [citation]. These are easily oxidized minerals that dissolve rapidly in the modern atmospheric environment, but were slowly eroded at the surface while exposed to air, like quartz grains in a river today.

=Great Oxidation Event=

The Great Oxidation Event, which occurred around 2.45 billion years ago in the Paleoproterozoic eon marks the first definitive Evidence: red beds, BIFs, sulfur isotopes

Source of o2: photosynthesis: cyanobacteria

Controversy over timing and Whiffs of oxygen

=Oxygen in the Proterozoic= When did the oceans oxygenate? Lomagundi excursion Canfield ocean hypothesis

=Phanerozoic variations in O2 level=

=Oxygen and the Evolution of Life=