How Oxygen Transformed Earth 2.4 Billion Years Ago

About 2.4 billion years ago, oxygen-making bacteria transformed Earth, killing much anaerobic life and helping trigger methane loss, global cooling, and a huge ice age.

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About 2.4 billion years ago, Earth underwent one of its most dramatic environmental transformations, known as the Great Oxidation Event. Cyanobacteria had evolved a form of photosynthesis that used water and sunlight while releasing oxygen as a by-product. At first, much of that oxygen was absorbed by minerals and dissolved substances in the oceans. Eventually, oxygen began accumulating and entering the atmosphere. The change was devastating for many organisms adapted to oxygen-free conditions. Oxygen is chemically reactive and could be toxic to anaerobic life, contributing to a major biological turnover. At the same time, atmospheric oxygen reacted with methane, reducing an important greenhouse gas and contributing to severe cooling. Geological evidence connects this period with major glaciation, including the Huronian glaciation, which is often estimated to have lasted roughly 300 million years. The oxygen revolution also opened new possibilities for life. Organisms that could use oxygen for respiration gained access to an efficient way of extracting energy, while oxygen-driven chemistry contributed to the formation of an ozone layer that helped shield Earth from harmful ultraviolet radiation. The long-term consequences helped shape the biological world that eventually included complex and multicellular life.

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