Plate Tectonics

History of the Theory First proposed by Alfred Wegener in 1912 Not widely accepted until the 1960s Proposes that Earth’s outer layer is composed of plates These layers move

Pangea Describes the arrangement of the continents millions of years ago as one huge supercontinent Helps explain how the same animals ended up so far apart from each other

Structure of the Earth core- innermost solid layer mantle- second layer containing the plastic asthenosphere and a solid rock layer comprising part of the lithosphere crust- thinnest outermost layer, includes part of the lithosphere

The rigid layer of the Earth is known as the lithosphere which is broken into plates These plates move across the asthenosphere

Force Behind Plate Tectonics The actual force behind plates tectonics is not known for certain. There are 2 possible theories: – Convection in the Earth’s mantle pushes the plates – Gravity pulls the older and heavier ocean floor with more force than the newer, lighter sections

Four Types of Boundaries There are 4 types of plate boundaries – Divergent – Convergent – Collision – Transform

Spreading Sea Floor The Atlantic Ocean is growing This occurs due to a divergent boundary in the middle of the Atlantic Ocean This boundary is the site of the Mid-Atlantic Ridge

Spreading Sea Floor As the plates move apart, magma from underneath the crust wells up between the space The seawater cools the exposed magma, forming rock, resulting in new sea floor

Continental Slide We know the Earth is not getting any bigger even though new crust is being created at the divergent boundaries There are also convergent boundaries where the crust of one plate slides under another

Subduction This process of one plate sliding under another is known as subduction As the crust subducts, it melts creating magma This magma can make its way to the surface and generate volcanoes Most of the world’s volcanoes occur at convergent boundaries

Continental Crush When an ocean plate meets a continental plate, subduction occurs However when two continental plates meet, they crush together in a collision boundary

Continental Crush This collision results in a folding and crumpling of the land A collision boundary results in mountain ranges such as the Himalayas

Sliding When a boundary neither consumes nor creates crust, it is known as a transform boundary Here the two plates are simply sliding past one another

Sliding As the two plates slide past each other, tension builds An earthquake results when this tension is released One of the most famous is the San Andreas Fault in California The western plate is moving northwest while the eastern plate is moving southeast

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