Introduction • Plate tectonics is the theory that Earth's outer layer is made up of plates, which have moved throughout Earth's history. • The theory explains the how and why behind mountains, volcanoes, and earthquakes.
Pangaea • 225 million years ago, all the major continents formed one giant supercontinent, called Pangaea. • Initiated by heat building up underneath the continent, Pangaea began to split apart, around 200 million years ago. These continents are still on the move today.
Theories of Plate Motion • Exactly what drives plate tectonics is not known. • One theory is that convection within the Earth's mantle pushes the plates. • Another theory is that gravity is pulling the older, heavier ocean floor with more force than the newer, lighter seafloor.
Plate Motion • Plate tectonic activity takes place at four types of boundaries: • Divergent boundaries • Convergent boundaries • Collisional boundaries • Transform boundaries
Divergent Boundaries • Also known as spreading boundary, it occurs where two plates move apart, allowing magma, to rise from the Earth's interior to fill in the gap. • The two plates move away from each other like two conveyor belts moving in opposite directions.
Convergent Boundaries • Also known as subduction boundary, it occurs where one plate slides under another as the two are pushed together. • If there is land at the edge of one of these plates, the ocean plate will subduct, or slide under that plate.
Collisional Boundaries • A collisional boundary occurs where two land masses on plates are pushed together. • Trying to occupy the same space, the land masses buckle and fold, creating mountain ranges.
Transform Boundaries • A transform boundary occurs where two plates slide against each other. • Rather than sliding smoothly, the plates build up tension, then release the tension with a spurt of movement called an earthquake
Birth of a Theory video questions • What led Wegener to his notion of continental drift? • What is and where does sea floor spreading occur? • How did paleomagnetism help support the notion of sea floor spreading? • What is a transform fault? • Why is plate tectonic theory called a “model that describes everything”?