Earth’s oldest rocks are 4.3 Ga; her oldest fossils are 3.5 Ga. Two long ice ages were in the Precambrian, with two more in the Paleozoic. At 1.4 Ga the western edge of North America was at Hells Canyon. Since then, exotic terranes have accreted, notably in the Klamaths, Wallowas, North Cascades, and Olympics. These surround the Columbia Embayment with its sedimentary and volcanic rocks. The last ice age began 2 Ma; during glacial periods the Pacific Northwest hosted both local glaciers and the Cordilleran Ice Sheet. Sea level changes accompanying alternating glaciations and interglaciations allowed humans to cross the Bering Land Bridge about 20 ka. Was the extinction of American megafauna about 10 ka caused by humans or by climate change at the end of the last glaciation? Fossil fuel combustion is melting glaciers and permafrost, leading to sea level rise and many other problems. A sixth ice age is not likely for at least 250 million years.

Presentation by Whitman Professor Emeritus Bob Carson. Talk begins at 4pm in the Grand Hall. Free to attend!