Plate Tectonics

By: Renee Moran

What Are Plate Tectonics?

A theory explaining the structure of the Earth's crust and many associated phenomena as resulting from the interaction of rigid lithospheric plates that move slowly over the underlying mantle. There are 12 major plates with a few minor once with in the major plates. (shown below)
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Make up of the Earth

The Earth is made up of three main layers; the crust, mantle, core

Crust- the rocky outer layer of Earth that we live on, it consists of less than 1% of Earths volume.

Mantle- the silicate rock rich in magnesium and iron under the crust. The mantle is more than two thousand miles thick and accounts for more than three-quarters of the volume of the Earth.

Core- the core is made up of an inner and outer layer. The solid inner core of iron and liquid outer core of nickel-iron alley.

Continental Drift

Is a scientific theory that the continents are always moving; it is the gradual movement of the continents across the earth's surface through geological time.

Alfred Wegener is credited with developing the hypothesis for continental drift.

Evidence for Continental drift

Alfred Wegener's primary sources of evidence included the fit of the continents, with the shores of the continents fitting together. Indicating that there once was a super continent known as Pangaea. Another part of key evidence is fossils that have been found on separate continents being the same.

Sea-floor spreading & who dicovered it

Harry Hess was one of the discoverers of sea-floor spreading and is credited with the discovery.

Sea floor is caused by two plates moving apart; this is caused by plate tectonics. Continental drift is also caused by plate tectonics. Therefore, we can conclude that continental drift is related to sea-floor spreading. When the plates move, it carries the continents with it and thus the continents drift away from each other. Sea-floor spreading is a result of divergent boundaries in the ocean crust.

How convection helps with plate tectonics

Convection helps with plate movement because convection currents inside of Earth's mantle are pushing the plates on the crust into and away fro each other. This is the main reason that the plates move and shift around. Convection currents make new crust and "recycle" the old.

Theory of Plate tectonics

The theory of plate tectonics is that the outer rigid layer of the earth is divided into a couple of dozen “plates” that move around across the earth’s surface relative to each other, like slabs of ice on a lake. It is the scientific theory that attempts to explain the movements of the Earth’s lithosphere that have formed the landscape features we see across the globe today.

Different types of boundaries


Transform boundaries is when two plate are sliding past each other this motion most commonly causes earthquakes. The most famous transform boundary in the world is the San Andreas Fault.


Divergent is when two plates that are diverging or are moving away from each other, this movement causes mainly rift valleys. Two very well-known rift valleys are the African rift and the Icelandic Rift. Earthquakes can also occur on the fault lines causing volcanoes.

Divergent (ocean)

Divergent in the ocean is when two plates are moving away from each other causing seafloor spreading. Most common is the Mid-Atlantic Ridge. A divergent boundary in the ocean is the main cause of seafloor spreading and continental drift.


Convergent boundaries is when two continental plates collide and push against each other. The result is mountains like the Himalayas.

convergent with subduction

Convergent with subduction is when an oceanic and continental plate collide and the oceanic plate sinks underneath (oceanic crust is thinner). This creates trenches that results in the Marianas trench. This process can also cause volcanoes that made the Hawaiian islands and the Andes Mountains both made by volcanoes as a result of convergent with subduction.

Ring of fire

The Ring of Fire is an area where a large number of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a 40,000 kilometer horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movement.

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