http://en.wikipedia.org/wiki/Great_Oxygenation_Event
The gap between the start of oxygen production from photosynthetic organisms and the geologically rapid increase in atmospheric oxygen (about 2.5–2.4 billion years ago) may have been as long as 900 million years. Several hypotheses might explain the time lag:
Tectonic trigger
The oxygen increase had to await tectonically driven changes in the Earth, including the appearance of shelf seas, where reduced organic carbon could reach the sediments and be buried.The newly produced oxygen was first consumed in various chemical reactions in the oceans, primarily with iron. Evidence is found in older rocks that contain massive banded iron formations that were apparently laid down as this iron and oxygen first combined; most of the planet's commercial iron ore is in these deposits.
Nickel famine
Chemosynthetic organisms were a source of methane, which was an important trap for molecular oxygen, because oxygen readily oxidizes methane to carbon dioxide(CO2) and water in the presence of UV radiation. Modern methanogens require nickel as an enzyme cofactor. As the Earth's crust cooled, the supply of nickel from volcanoes was reduced and less methane was produced. This allowed the oxygen concentration in the atmosphere to increase. From 2.7 to 2.4 billion years ago, the levels of nickel deposited declined steadily; it was originally 400 times today's levels.
Bistability
A 2006 theory, called bistability, comes from a mathematical model of the atmosphere. In this model, UV shielding decreases the rate of methane oxidation once oxygen levels are sufficient to support the formation of an ozone layer. This explanation proposes an atmospheric system with two steady states, one with lower (0.02%) atmospheric oxygen content, and the other with higher (21% or more) oxygen content. The Great Oxidation can then be understood as a switch between lower and upper stable steady states.
Role in mineral diversification
Recent research has shown that the Great Oxygenation Event triggered an explosive growth in the diversity of minerals on Earth. It is estimated that this event alone was directly responsible for more than 2,500 new minerals of the total of about 4,500 minerals found on Earth. Most of these new minerals were hydrated, oxidized forms of minerals formed due to dynamic mantle and crust processes after the Great Oxygenation event.
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