Snowball Earth - History

History

Douglas Mawson (1882–1958), an Australian geologist and Antarctic explorer, spent much of his career studying the Neoproterozoic stratigraphy of South Australia where he identified thick and extensive glacial sediments and late in his career speculated about the possibility of global glaciation.

Mawson's ideas of global glaciation, however, were based on the mistaken assumption that the geographic position of Australia, and that of other continents where low-latitude glacial deposits are found, has remained constant through time. With the advancement of the continental drift hypothesis, and eventually plate tectonic theory, came an easier explanation for the glaciogenic sediments—they were deposited at a point in time when the continents were at higher latitudes.

In 1964, the idea of global-scale glaciation reemerged when W. Brian Harland published a paper in which he presented palaeomagnetic data showing that glacial tillites in Svalbard and Greenland were deposited at tropical latitudes. From this palaeomagnetic data, and the sedimentological evidence that the glacial sediments interrupt successions of rocks commonly associated with tropical to temperate latitudes, he argued for an ice age that was so extreme that it resulted in the deposition of marine glacial rocks in the tropics.

In the 1960s, Mikhail Budyko, a Russian climatologist, developed a simple energy-balance climate model to investigate the effect of ice cover on global climate. Using this model, Budyko found that if ice sheets advanced far enough out of the polar regions, a feedback loop ensued where the increased reflectiveness (albedo) of the ice led to further cooling and the formation of more ice, until the entire Earth was covered in ice and stabilized in a new ice-covered equilibrium. While Budyko's model showed that this ice-albedo stability could happen, he concluded that it had never happened, because his model offered no way to escape from such a scenario.

The term "Snowball Earth" was coined by Joseph Kirschvink, a professor of geobiology at the California Institute of Technology, in a short paper published in 1992 within a lengthy volume concerning the biology of the Proterozoic eon. The major contributions from this work were: (1) the recognition that the presence of banded iron formations is consistent with such a glacial episode and (2) the introduction of a mechanism with which to escape from an ice-covered Earth—the accumulation of CO₂ from volcanic outgassing leading to an ultra-greenhouse effect.

Franklyn Van Houten's discovery of a consistent geological pattern in which lake levels rose and fell is now known as the "Van Houten cycle." His studies of phosphorus deposits and banded iron formations in sediments made him an early adherent of the "Snowball Earth" hypothesis postulating that the planet's surface froze more than 650 million years ago.

Interest in the Snowball Earth increased dramatically after Paul F. Hoffman, professor of geology at Harvard University, and coauthors applied Kirschvink's ideas to a succession of Neoproterozoic sediments in Namibia, elaborated upon the hypothesis by incorporating such observations as the occurrence of cap carbonates, and published their results in the journal Science in 1998.

Currently, aspects of the hypothesis remain controversial and it is being debated under the auspices of the International Geoscience Programme (IGCP) Project 512: Neoproterozoic Ice Ages.

In March 2010, the journal Science published an article "Calibrating the Cryogenian" which concluded that "Ice was therefore grounded below sea level at very low paleolatitudes, which implies that the Sturtian glaciation was global in extent". A popular account of this conclusion was published in Science Daily.