<P> Firstly, it oxidized atmospheric methane (a strong greenhouse gas) to carbon dioxide (a weaker one) and water . This decreased the greenhouse effect of the Earth's atmosphere, causing planetary cooling, and triggered the Huronian glaciation . Starting around 2.4 billion years ago, this lasted 300 - 400 million years, and may have been the longest ever snowball Earth episode . </P> <P> Secondly, 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 available to living organisms, with global environmental impacts . For example, mitochondria evolved after the GOE, giving organisms the energy to exploit new, more complex morphologies interacting in increasingly complex ecosystems . </P> <P> There may have been a gap of up to 900 million years between the start of photosynthetic oxygen production and the geologically rapid increase in atmospheric oxygen about 2.5--2.4 billion years ago . Several hypotheses propose to explain this time lag . </P> <P> 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 apparently laid down as this iron and oxygen first combined; most present - day iron ore lies in these deposits . Evidence suggests oxygen levels spiked each time smaller land masses collided to form a super-continent . Tectonic pressure thrust up mountain chains, which eroded to release nutrients into the ocean to feed photosynthetic cyanobacteria . </P>

Explain how rising atmospheric concentrations of oxygen affected life on earth