Timing of the GOE.

http://en.wikipedia.org/wiki/Oxygen_catastrophe

The most widely accepted chronology of the Great Oxygenation Event suggests that free oxygen was first produced by prokaryotic and then later eukaryotic organisms that carried out oxygenic photosynthesis, producing oxygen as a waste product. These organisms lived long before the GOE, perhaps as early as 3500 million years ago.

The oxygen they produced would have quickly been removed from the atmosphere by the weathering of reduced minerals, most notably iron. This 'mass rusting' led to the deposition of iron(III) oxide to form banded-iron formations such as those sediments in Minnesota and Pilbara, Western Australia.

Oxygen only began to persist in the atmosphere in small quantities shortly (~50 million years) before the start of the GOE. Without a draw-down, oxygen could accumulate very rapidly.

For example, at today's rates of photosynthesis (which are much greater than those in the land-plant-free Precambrian), modern atmospheric O₂ levels could be produced in around 2,000 years.

Another hypothesis is an interpretation of the supposed oxygen indicator, mass-independent fractionation of sulfur isotopes, used in previous studies, and that oxygen producers did not evolve until right before the major rise in atmospheric oxygen concentration. This hypothesis would eliminate the need to explain a lag in time between the evolution of oxyphotosynthetic microbes and the rise in free oxygen.

Either way, the oxygen did eventually accumulate in the atmosphere, with two major consequences. First, it oxidized atmospheric methane (a strong greenhouse gas) to carbon dioxide (a weaker one) and water, triggering the Huronian glaciation.

The latter may have been a full-blown, and possibly the longest ever, snowball Earth episode, lasting 300–400 million years. Second, the increased oxygen concentrations provided a new opportunity for biological diversification, as well as tremendous changes in the nature of chemical interactions between rocks, sand,clay, and other geological substrates and the Earth's air, oceans, and other surface waters.

Despite the natural recycling of organic matter, life had remained energetically limited until the widespread availability of oxygen. This breakthrough in metabolic evolution greatly increased the free energy supply to living organisms, having a truly global environmental impact; mitochondria evolved after the GOE.