Paleontology and geologyMost of Ontario is underlain by Precambrian rocks of the Canadian Shield. These igneous, metamorphic, and sedimentary rocks represent the remains of ancient continents, islands, volcanoes, and ocean basins. Today they form the core of the North American continent and are divided into geologic provinces based on their shared geologic history. The Superior Province in the north contains the oldest rocks, dating back to 3.0 Ga, and the Grenville Province in the southeast is the youngest, from 1.3 Ga. Lying in between and of intermediate age, the Southern Province contains some of the most interesting geologic features. The Sudbury Structure is a buried impact crater from an asteroid that hit the Earth 1.85 Ga. It is the second largest impact crater known on the planet. Exposed around Lake Superior, the multi-colored Gunflint Chert was deposited in an ancient sea and contains stromatolites, as well as exceptionally preserved fossils of algae and fungi. At two billion years old, these microscopic spheres, flasks, and filaments are the oldest known fossils. In the east, some rocks show evidence of ancient glaciers that covered the early continent. All these rocks have been metamorphosed to some degree over the millions (in some cases billions) of years since they formed, and many of them are mined for their economically important deposits of gold, silver, copper, uranium, nickel, iron, lead, zinc, and diamonds. |
