when did the canadian shield begin to form
Canadian Shield The Canadian Shield is among the oldest on earth, with regions dating from 2.5 to 4.2 billion years.[8] The multitude of rivers and lakes in the entire region is caused by the watersheds of the area being so young and in a state of sorting themselves out with the added effect of post-glacial rebound. The Shield was originally an area of very large, very tall mountains (about 12,000 metres or 39,000 feet)[9] with much volcanic activity, but over hundreds of millions of years, the area has been eroded to its current topographic appearance of relatively low relief.[citation needed] It has some of the oldest (extinct) volcanoes on the planet.[citation needed] It has over 150 volcanic belts (now deformed and eroded down to nearly flat plains) whose bedrock ranges from 600 to 1200 million years old.[citation needed]