Plate Tectonic Notes

• Earth’s Layers: • Crust • Mantle • Core

Earth’s Layers

• Crust Lithosphere outermost layer that is the tectonic plates but does have some mantle rock

• Mantle – 2 Parts Asthenosphere: (solid, soft layer that moves slowly) The layer that the tectonic plates move on Mesosphere: solid lower part of the mantle

• Core – Outer core (liquid iron and nickel) – Inner core (solid iron and nickel)

Earth’s plates

Pangaea- Supercontinent that once existed on Earth around 245 million years ago…

Plate Movement • Continental Drift

– Lithosphere (tectonic plates) is divided into plates that slide around on top of the slowly moving asthenosphere

– It occurred after the break-up of Pangaea, and since then the continents have drifted apart

Theory of Continental Drift

– Alfred Wegener (early 1900’s) was the first to discuss the theory of Pangaea and continental drift.

– Theory of Pangaea- claimed that the continents had formed a single land mass which has split apart over time.

– Wegner was not the first to suggest this theory, but he was the first to present information from several fields.

– Continental Drift Theory – Was that all of the continents were once joined together, but over time have drifted apart.,

– Pangea – name of the supercontinent that contained all land on Earth

Evidence of Continental Drift

• Evidence of Wegner’s theory:

– Similar glacier deposits in South America and Africa, and fossil findings

– The outlines of the continents fit with each other. – Mountain ranges line up between Africa and South America.

How does continental drift work?

- Plates compress or pull apart from each other

• Plates collide = convergent boundary • Plates separate = divergent boundary • Plates slide past one another horizontally = transform

boundary • Subduction zone = one plate slides under another

Convergent Boundary

Subduction Zone

• When an oceanic plate slides under a continental plate.

• Plates collide while moving towards each other

• When both plates are continental plates, the plates push against each other, creating mountain ranges.

Cause: oceanic trenches, and can cause volcanoes to form due to the oceanic plate melting and creating pressure under the continental plate.

Divergent Boundary

• Plates separate (pull apart)

Sea Floor Spreading Theory

• Harry Hess formulated the idea of sea floor spreading in 1962. • Sea Floor Spreading Theory- idea that the seafloor moves and

carries the continents with it. • Caused by divergent boundaries moving apart and allowing the liquid

like asthenosphere to move upward and cool creating new oceanic crust.

Transform Boundary

When plates pull away from one another they form: sea floor spreading, mid-oceanic ridges or rift valleys

• Plates slide past

one another horizontally

• These areas are likely to cause earthquakes, and volcanic action, and fault lines.

What is the force moving Plate tectonics: CONVECTION CURRENTS

- Convection currents in the mantle are what causes the movement of tectonic plates. - As the extremely hot molten material from the mantle rises toward the crust, it cools enough to become denser and sink back into the hotter area of the mantle.

- The process repeats (cycles) continually.

Rock does two things when stress is placed on it. It can fold or fault (break). When plates push against one another, they form MOUNTAINS.

• Folded Mountains – made when rock is squeezed together and pushed upward

Fault – broken rock layers resulting from stress

• These mainly occur around transform boundaries

• They are due to stress from tectonic plate movement.

Ring Of Fire

• 90% of the world's earthquakes and 89% of the world's largest

earthquakes occur along the Ring of Fire in the Pacific Ocean from California around to India – Caused by subduction zones.