OI Colloquium
Dr. Nick Eyles
 University of Toronto, Department of Geology
Title Planet Earth’s icy legacy: glacio-epochs of the ancient past
Date19 / 11 / 2007
Time 2:30pm (Coffee served at 2:15pm)
Abstract The nineteenth century discovery of rocks recording ancient ice ages early in Earth’s history destroyed the simple notion of a hot early Earth that is steadily cooling; the discipline of paleoclimatology was born. There is now evidence of six lengthy episodes of cold climate where extensive ice covers existed for many millions of years (glacio-epochs). The oldest occurs during the Archean around 2.8 billion (Ga) years ago, followed at 2.4 Ga in the Paleoproterozoic, in the Neoproterozoic between 750 to c. 600 million years ago (Ma), briefly in the Early Paleozoic around 440 Ma, the Late Paleozoic (350 to 250 Ma, the longest of all) and the Cenozoic beginning some 40 million years ago when ice began to form at both poles. It is now apparent that these icy phases are primarily the product of long-term climate change driven by tectonic processes reordering the planet's landmasses and oceans, and are closely linked to the cyclic formation and breakup of supercontinents. Some glacio-epochs are triggered during the formation of supercontinents when plate collisions created high mountains (tectonotopography) but the strongest link is with supercontinent breakup when rifting created broad areas of elevated crust. Ice masses expand to continental scale ice sheets if other conditions (e.g., moisture sources, paleolatitude, pCO2, Milankovitch ‘astronomical variables’) allow. This talk examines Earth’s episodic flirtation with cold, examines how such episodes are recognised and shows how the rock record provides a picture of the Neoproterozoic glacio-epoch very different from the Snowball Earth hypothesis of a permanently frozen planet.

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