The largest region of Canada, comprising 48% of the surface land (4.8 million km2), the Canadian Shield is home to some of the oldest rocks on earth and considered to be the nucleus of the North American continent. Composed of the roots of ancient mountain ranges, its Gneiss and Granite rocks extend back in time 4 billion years, nearly to the age of the earth itself. Geologically, this region has been stable for the past one billion years, shielded from the forces of Plate Tectonics, enabling its surface to become relatively level.
One exception to this lays along the East Coast of Labrador and Baffin Island where the opening of the Atlantic uplifted this coastal plateau to elevations of 800 -1500 m above sea level. These rolling highlands were deeply cut by glacial troughs creating Fjord like topography along the coast. Most of the shield however is both lower in elevation and relatively level, as numerous advances and retreats of glaciers (75,000 - 6,000 years ago) scraped its surface creating the characteristic pocked marked shallow lake basins, and leaving only a thin layer of soil to support a boreal forest habitat.