You find the ages of the heartland of the Canadian
Shield in the bottom, old part of the table, and of the younger
ones in its upper part, and, on the map we just saw, toward the
edges of the continent.
The oldest continental crust originally was transformed from colliding
plates of oceanic crust which eventually became stable cratons,
the foundations of a growing continent. The North American craton
is one of the oldest, and probably the largest, craton in the world.
Its core is the heartland of our continent.
|
