The rocks that form the Canadian Shield were formed about four billion
years ago during the Archeon Eon of the Precambrian Era. Erosion of
this extremely rugged, mountainous landscape deposited enormous
quantities of clays, silts, sands and gravels into the surrounding
waters. Compressed by their sheer cumulative weight and the heat of the
shifting Earth's crust, sedimentary and metamorphic rocks formed during
the Proterozoic Eon of the Precambrian Era.
A significant event ocurred when a large crater was formed. Two theories exist on the origin of the crater: the first is that a meteor slammed into the region; the second that it is the result of a huge volcanic explosion. The movement of the Proterozoic rocks northward along the Grenville Front compressed the crater into the present day oval shape. The Sudbury basin is the richest deposit of nickel ore in the world.
More recent rocks that were formed above these ancient layers have since been largely removed by the scouring action of glaciers that covered northern North America in the several ice ages in the past 100,000 years.
The last ice age scraped the rocks in a NNE (north-north-east) to SSE (south-south-east) direction. At the end of the last ice age, all the waters in the Sudbury area (and the great lakes) drained to the east, toward the Ottawa River. After the weight of the glaciers left this area, the land slowly began to rise. The surface rose about 20 metres at the eastern end of Lake Nipissing, and the French River began flowing to the west into Georgian Bay. The soil on which trees and other vegetation grow in this part of the continent are the result of gradual sediment buildup since the last ice age.
More history of Sudbury