Theory of plate tectonics

Theory of plate Theory of plate tectonicstectonics

Continental drift hypothesisContinental drift hypothesis Before the theory of plate tectonics Before the theory of plate tectonics

in the 1960’s, there was Alfred in the 1960’s, there was Alfred Wegener’s hypothesis of continental Wegener’s hypothesis of continental drift.drift.

He thought all the continents were He thought all the continents were once connected to make a single once connected to make a single supercontinent called Pangea.supercontinent called Pangea.

Pangea 300 million years Pangea 300 million years agoago

Evidence that supported Evidence that supported PangeaPangea

Why do the continents move?Why do the continents move?

The theory of plate tectonics states that the The theory of plate tectonics states that the Earth’s lithosphere is broken up into plates. Earth’s lithosphere is broken up into plates. These plates continually move and change These plates continually move and change shape and size.shape and size.

When plates move, they cause earthquakes When plates move, they cause earthquakes and volcanoes along the plate boundaries.and volcanoes along the plate boundaries.

Plates move slow-on average 5 cm a year!Plates move slow-on average 5 cm a year! Plate motion is caused by convective Plate motion is caused by convective

currents in the asthenospherecurrents in the asthenosphere

Types of plate boundariesTypes of plate boundaries Divergent- plates pull apartDivergent- plates pull apart Real life example: atlantic ocean and Real life example: atlantic ocean and

east african rift valleyeast african rift valley Causes: earthquakes, sea floor Causes: earthquakes, sea floor

spreading, rift valleys, and mid ocean spreading, rift valleys, and mid ocean ridgesridges

divergentdivergent Mid ocean ridgeMid ocean ridge East African rift East African rift

valleyvalley

Convergent continental Convergent continental continentalcontinental

2 continents collide-push together2 continents collide-push together Example: how Appalachian Example: how Appalachian

mountains formed and the mountains formed and the Himalayan mountainsHimalayan mountains

Causes earthquakes and mountainsCauses earthquakes and mountains

Appalachian Appalachian mountains formmountains form

Himalayan Himalayan mountainsmountains

Convergent oceanic oceanicConvergent oceanic oceanic 2 ocean plates collide-push together2 ocean plates collide-push together Example: islands of japan, indonesiaExample: islands of japan, indonesia Causes: earthquakes, subduction Causes: earthquakes, subduction

zones, tsunamis, volcanic islandszones, tsunamis, volcanic islands

Convergent oceanic Convergent oceanic continentalcontinental

An ocean plate and continental plate An ocean plate and continental plate collidecollide

Examples: Cascade volcanic Examples: Cascade volcanic mountains in northwestern US (Mt st mountains in northwestern US (Mt st Helens)Helens)

Causes: earthquakes, volcanic Causes: earthquakes, volcanic eruptions, tsunamiseruptions, tsunamis

Transform faultTransform fault 2 plates slide past each other2 plates slide past each other Example: San andreas fault in Example: San andreas fault in

CaliforniaCalifornia Causes only earthquakesCauses only earthquakes

What evidence supports the What evidence supports the theory of plate tectonics?theory of plate tectonics?

Paleomagnetism- alternating layers Paleomagnetism- alternating layers of rock at the bottom of ocean floors of rock at the bottom of ocean floors show normal and reverse polarityshow normal and reverse polarity

Earthquake patternsEarthquake patterns

Hot spotsHot spots