Great Oxidation Event and Snowball Earth

Abstract

The atmosphere of early Earth contained little molecular oxygen. A significant increase in oxygen occurred ca. 2.4–2.0 billion years ago in what is called the Great Oxidation Event (GOE). A large positive excursion in carbon isotopic composition in sedimentary carbonates is known to have occurred 2.2–2.0 billion years ago (the Lomagundi-Jatuli event), which provides evidence for an enhanced rate of organic carbon burial, i.e., enhanced net production of oxygen. The Proterozoic snowball Earth event (global glaciation) occurred 2.3–2.2 billion years ago, roughly coinciding with the GOE. Thus, a causal relationship between the GOE and the snowball Earth event has been suggested. The snowball Earth event could have been triggered by an increase in oxygen in the atmosphere because it would have resulted in a significant reduction of atmospheric methane level, thereby reducing the greenhouse effect of the atmosphere and causing global glaciation. On the other hand, termination of the snowball Earth event may have triggered the production of a large amount of oxygen because the extremely hot climate (~60 °C) immediately after the termination of the snowball Earth event must have significantly increased the supply of phosphate to the oceans, resulting in large-scale blooms of cyanobacteria, which could have produced large amounts of oxygen. The postglacial transition of atmospheric oxygen levels may have promoted an ecological shift and biological innovations for oxygen-dependent life.