The Paleoproterozoic Snowball Earth and the Rise of Oxygen

What was the nature of the transition from an anoxic to an oxygenated Earth?

In the Archean eon, three billion years ago, Earth?s atmosphere was free of oxygen. This absence is reflected in numerous proxies, particularly the record of mass-independent fractionation of sulfur isotopes (Farquhar and Wing, 2003). By two billion years ago, in the middle of the Paleoproterozoic era, many proxies suggest that oxygen had built up to a small but significant level in the atmosphere. Aside from the origin of life itself, the transition from the anoxic Archean to the oxic Proterozoic is the most radical change to occur to occur in the history of the Earth system.

Some researchers suggest that this transition occurred gradually, perhaps driven by a slight change in the oxidation state of the mantle or the onset of plate tectonics. Based on a critical analysis of the available data, with a strong dose of caution applied to the use of uniformitarian interpretations in such a radically different world, Joe Kirschvink (Caltech) and I have suggested instead that the transition occurred rapidly (Kopp et al., 2005). We propose that the Makganyene Snowball Earth event, which occurred at ~2.3 billion years ago, was a direct consequence of the transition. During the Snowball Earth, the presence of which is indicated by glacial deposits with low paleolatitudes from the Transvaal Supergroup in South Africa (Evans et al., 1997), the entire planet may have been sheathed in ice for tens of millions of years.

Based on a simple biogeochemical flux model I constructed, if the Archean Earth was kept warm by a methane greenhouse (Kasting, 2005), then the evolution of oxygenic photosynthesis could have triggered a Snowball Earth event on a time scale as short as about a million years (Kopp et al., 2005). Rather than a gradual transition, the anoxic-to-oxic transition, triggered by a chance evolution occurrence, may have been a catastrophic event: the world?s first biologically-caused climate disaster.

This hypothesis is an end-member hypothesis, but it is testable and serves to motivate research in this critical interval in Earth history.

Related Publications

• M. Liang, H. Hartman, R. E. Kopp, J. L. Kirschvink, and Y. L. Yung (2006). Production of hydrogen peroxide in the atmosphere of a Snowball Earth and the origin of oxygenic photosynthesis. Proc. Natl. Acad. Sci. 103: 18896-18899. doi:10.1073/pnas.0608839103 [Journal link]
• R. E. Kopp, J. L. Kirschvink, I. A, Hilburn, and C. Z. Nash (2005). The Paleoproterozoic Snowball Earth: A climate disaster triggered by the evolution of oxygenic photosynthesis. Proc. Natl. Acad. Sci. 102: 11131-11136. doi:10.1073/pnas.0504878102 [Journal link]