Plate tectonics
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Plate Tectonics. Pangea. A scientist named Alfred Wegener proposed that continents were once all together as one large continent called Pangea . He proposed that they drifted apart in a process that is now called continental drift. Pangea. His hypothesis was supported by:

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Plate Tectonics

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Plate tectonics

Plate Tectonics



A scientist named Alfred Wegener proposed that continents were once all together as one large continent called Pangea.

He proposed that they drifted apart in a process that is now called continental drift.



His hypothesis was supported by:

The fit of coastlines

Distribution of Paleozoic glaciers

Distribution of Paleozoic equatorial climatic belts.

Distribution of fossil species

Match-up of distinctive rock assemblies on both sides of the ocean.



Paleomagnetism is the study of rocks and the record of the Earth’s magnetic field.

Paleomagnetism allowed scientists to suggest the apparent polar-wander paths of the north and south pole.

These apparent polar-wander paths are different for each continent.

This could explain the movement of continents while the poles remain fixed.



Geologists have documented that the Earth’s magnetic field reverses polarity every now and then.

This is called magnetic-reversal chronology.

Continental drift

Continental Drift

Harry Hess proposed the idea of sea floor spreading.

He suggested that new sea floor forms at mid-ocean ridges through the upwelling of molten rock.

Eventually the ocean floor sinks back into the Earth at subduction zones.

Evidence of sea-floor spreading comes from marine magnetic anomalies and drilling of the sea floor.

Plate tectonics1

Plate Tectonics

The earth has an outermost layer called the lithosphere which is broken into discrete plates that move relative to each other.

Plates are made of the crust and upper mantle.

Plate tectonics2

Plate Tectonics

Most earthquakes and volcanoes occur along these plate boundaries. They are not as common within the interior of the plates, but can occur.

Plate tectonics3

Plate Tectonics

There are three types of plate boundaries:

Divergent-found at mid-ocean ridges. Sea floor spreading takes place with new oceanic lithosphere.

Convergent-marked by deep-ocean trenches and volcanic arcs. The oceanic lithosphere is subducted beneath an overriding plate.

Transform-marked by large faults where one plate slides past another. No new plate is formed and no plate is destroyed.

Plate tectonics4

Plate Tectonics

Triple junctions occur where three plate boundaries intersect.

Hot spots are places where volcanism occurs at an isolated volcano. Often the plate is over a mantle plume. When the plate moves, the volcano dies and another volcano forms where the extinct volcano once was.

Plate tectonics5

Plate Tectonics

Rifting can cause a continent to split into smaller pieces. The continent stretches and thins.

If this continues, a new mid-ocean ridge can form.

Plate tectonics6

Plate Tectonics

Convergent plate boundaries become nonexistent when a piece of crust moves into a subduction zone.

This causes collision.

Plate tectonics7

Plate Tectonics

Ridge-push and slab pull contribute to plate tectonics.

Convection can also contribute to plate tectonics, but it is not the driving force.

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