Australia: The Land Where Time Began

A biography of the Australian continent 

Snowball or Slushball Earth

The term "snowball Earth" was coined by Joseph Kirschvink in 1992. In 1998 a team of Harvard geoscientists published a paper in Science (Science, 28 August 1998, p. 1342) in which they suggested that more than 500 Ma the entire Earth was glaciated from pole to pole. Not all researchers accept the proposal that the Earth was completely frozen over, some suggesting it was more likely to be a case slushball Earth than a snowball Earth, though they still believe it was probably profoundly cold, just not completely frozen. Basing their work on simple climate modelling the authors of the 1998 paper came to the conclusion that if any ice that extended as far as the tropical regions about 652 Ma during the Marinoan Glaciation, it would continue to extend to the equator, as the greatly increased reflective surface would trigger a climatic feedback which would intensify the glaciation until it was global, a hard snowball.

The use of more recent modelling suggests that though the models can get terrestrial glaciers in the tropics the modelers have not been successful at also getting a full snowball Earth, the models indicating that it may not be possible to freeze the tropical oceans. One reason for this is that the models of the oceans can hold large amounts of heat which can be moved around by currents, making a complete freeze over difficult or impossible.

A "thin ice" snowball Earth has been suggested by James Kasting, an atmospheric physicist of PSU, he and David Pollard, a modeler at PSU considered how thick ice intruding from higher latitudes might be held off by a continent poleward of an inland sea, preserving small areas of thin ice on the oceans that allowed sunlight through to be used by marine plants, the researchers believing all the constraints are better satisfied by a thin ice model than in other models.

According to Philip Allen of Imperial College London most geological scientists now reject the suggestion that the entire Earth froze over. What scientists studying the possibility of a snowball Earth during the Marinoan Glaciation have discovered is evidence in the sediments from that time of water and ice  moving around, ocean currents that were flowing, as well as waves on an open ocean, not the stagnation expected. Supporters of the hard ice snowball Earth have suggested that the new evidence may reflect conditions Just before of just after a hard snowball. According to the author1 most geochemists oppose a snowball. One of the key factors in the 1998 proposal was a bizarre chemical deposit found on top of the cap carbonate formation, glacial deposits, the suggestion being that it could have formed following a glacial period only if the atmosphere and the world ocean were sealed off from each other for millions of years. According to this proposal the biota of the oceans could have continued to survive because of rare cracks in the ice, or volcanic hotspots that kept the water above them ice free. Following study of the isotopic records of carbon, strontium and sulphur, Alan Jay Kaufman of the University of Maryland, a co-author of the 1998 paper in Science, has concluded that the slushball best fits evidence that has accumulated, the sulphur isotopes in particular indicating that the open water was greater than ice cracks.

See Cryogenian Dating

Sources & Further reading

  1. Kerr, Richard A. "Snowball Earth Has Melted Back to a Profound Wintry Mix." Science 327, no. 5970 (March 5, 2010 2010): 1186.
  2. Macdonald, Francis A., Mark D. Schmitz, James L. Crowley, Charles F. Roots, David S. Jones, Adam C. Maloof, Justin V. Strauss, et al. "Calibrating the Cryogenian." Science 327, no. 5970 (March 5, 2010 2010): 1241-43.


Author: M. H. Monroe
Last updated 29/12/2012 

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