24. Lithospheric Plates and Plate Movement

Photo 43: Plate movement of the Earth, Tyrrell Museum, Drumheller, Alberta. 2011-05-12

Pangaea

Nearly a century ago, Alfred Wegener already hypothesized continental movement and an initial supercontinent. The shields of the current continents, like the Canadian shield, are the solid core of continents and maintain relative size and shape throughout time. In 1915, Wegener named this supercontinent Pangaea (meaning ‘All-Earth’). He theorized that Pangaea broke apart into the northern Laurasia (North America and Eurasia) and the southern Gondwanaland (South America, Africa, India, Australia, and Antarctica). At the Royal Tyrrell Museum in Drumheller, the exhibition showed the moving continents per era (photo 43).

Plates

The Mid-Oceanic Ridge system is a mountainous area in the middle of the Atlantic and Pacific Oceans. The mountain peaks are till about 2 km underneath sea-level, however. These mountains are unlike continental mountains. The ridge system is the result of seafloor spreading, where new continental crust is created by magma from the Earth’s upper mantle due to plates moving away from each other. These plates are called lithospheric plates and the movement of the plates is called plate tectonics. Plate margins are the places, opposite of seafloor spreading, where the plates collide. In Europe, this creates the Trans-Eurasian belt of mountains. In the Pacific Ocean, this is the ring of fire, the chain of earthquake and volcanoes along the Asian and American coasts. Japan’s recent earthquake was one in the ring of fire earthquake zone. In Alberta, colliding plates have created the Rocky Mountains (photo 44).

Photo 44: Continental convergence zone, the Rocky Mountains of Alberta. 2008-06-29