Plate Tectonics Theory
Plate boundaries
A plate boundary exists where the tectonic plates meet. The plates move apart, together, and past each other.
Transform plate boundaries
As two plates move past each other, the plates get stuck, stop moving and build up stress. Eventually, the stress is too great and the rocks break, suddenly moving apart. This results in a rapid release of energy as earthquakes.
Ridge push
Because mid ocean ridges are higher, gravity pulls the surrounding rocks down and away for the ridge. Ridge push moves lithosphere in opposite directions away from the ridge.
Evidence for plate tectonics
By keeping track of the distance between satellites and Earth, it is possible to determine how fast a tectonic plate moves. The theory of plate tectonics provides an explanation for why earthquakes and volcanos occur in certain places. When plates separate, collide, or slide past each other, stress builds.
Basal drag
Convection currents in the mantle produce a force that causes motion called basal drag. Convection currents in the asthenosphere circulate and drag the lithosphere.
Forces causing plate motion
Convection occurs in the mantle underneath Earth's tectonic plates. Three forces act on the plates to make them move: basal drag from convection currents, ridge push at mid-ocean ridges, and slab pull from subducting plates.
Tectonic plates
Earth's tectonic plates are large pieces of lithosphere that fit together like a jigsaw puzzle. The asthenosphere, under the lithosphere, is so hot is enables the plates to move because the material under can flow. The interactions between the lithosphere and the asthenosphere help to explain plate tectonics.
Divergent plate boundaries
Mid-ocean ridges are located along divergent plate boundaries. Divergent plate boundaries can also exists in the middle of a continent. They pull plates apart and form rift valleys.
Convection currents
Plate tectonic activity is related to convection in the mantle. These currents in the asthenosphere move the lithosphere above.
Ridge push
Rising mantle material at mid-ocean ridges creates the potential for plates to move away from the ridge with a this force.
A theory in process
The investigation that Wegener began nearly a century ago is still being revised. Plate tectonics explain the connection between continental drift and the formation and destruction of crust along plate boundaries.
Plate motion
The main objection to Wegener's continental drift hypothesis was that he could not explain why or how they move. Scientists now understand that continents move because the asthenosphere moves underneath the lithosphere.
Plate Tectonics Theory
The theory of plate tectonics suggests that Earth's surface is divided into large plates of rigid rock. Each plate moves over Earth's hot and semi-plastic mantle. Plate tectonics provides an explanation for the occurrence of earthquakes and volcanic eruptions.
Convergent plate boundary
These form where two plates collide.
Divergent plate boundary
This forms where two plates separate.
Transform plate boundary
This forms where two plates slide past each other.
Slab pull
This is a force that's caused by a slab sinking and pulls on the rest of the plate.
Subduction
This is a process where the denser plate sinks below the more buoyant plate.
Convection
This is the circulation of material caused by differences in temperature and density.
Lithosphere
This is the cold and rigid outermost rock layer.
Convergent plate boundaries
When an oceanic plate and a continental plate collide, the denser oceanic plate subduction under the edge of the continent and creates a deep ocean trench. The older and denser oceanic plate will subduct under the younger oceanic plate and create a deep ocean trench and an island arc. When two plates collide, neither plate is subducted, and mountains such as the Himalayas form.
Slab pull
When tectonic plates collide, the denser plate (slab) will sink into the mantle along a subduction zone. Because the slab is old and cold, it's denser than the surrounding mantle and will sink.
