The Theory of Plate Tectonics

• ​Crust

• ​Mantle

• ​Core

• Lithosphere

• ​Asthenosphere

• ​Mesopshere

• ​Outer Core

• ​Inner Core

• ​Alfred Wegner came up with the Theory of Continental Drift in 1915.

• ​He believed the continents were once all part of a super-continent he called "Pangea" meaning "all Earth,"

• ​The Crust/Lithosphere is divided into tectonic plates.

• ​These tectonic plates are always moving, but very slowly

• ​The edges where the plates meet are called plate boundaries

• Divergent

• ​Convergent

• ​Transform

• ​Convergent boundaries are where two plates are coming together, or "converging"

• ​This is how mountains form!

• ​Subduction also occurs at convergent boundaries

• ​This is where one plate "subducts" or goes underneath the other plate - this is called a "subduction zone"

• ​This causes volcanoes!

• ​(The Ring of Fire is a major subduction zone in the Pacific Ocean with lots of volcanoes)

• ​Transform boundaries are where two plates are grinding against each other

• Fault lines are cracks in the crust where earthquakes often occur.

• ​A famous fault line with lots of earthquakes is San Andreas Fault in California

Divergent Boundaries

• ​Divergent boundaries are where plates move apart from each other

• ​This can create rift valleys (and split apart continents- like Africa!)

• ​In the ocean where the crust is very thin, magma pushes through where the plates are moving apart.

• ​This forms the Mid-Atlantic ridge, a chain of underwater "mountains" and causes a process called sea floor spreading