Plate Tectonics

By Ms. Neumann & Mrs. Fraser

The Movement of Earth

• Earth’s Layers:• Crust

• Mantle

• Core

Earth’s Layers

• Crust– Lithosphere

(outermost, but does have some mantle rock) layer that is the tectonic plates

Earth’s Layers• Mantle

– Asthenosphere (solid, soft layer that moves slowly) layer that the tectonic plates move on

– Mesosphere (solid lower part of mantle)

Earth’s Layers• 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.

Alfred Wegener’s Theory

• 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

• His theory was very controversial. It was disproved at the time since Wegener could not explain how the continents were drifting apart.

Proof 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.

Continental Drift over time

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

• Plates collide while moving towards each other

Converging...They Crash! And they’re both Continental Plates• When both are continental plates, the plates

push against each other, creating mountain ranges.

Subduction Zone

• When a oceanic plate slides under a continental plate.

Subduction Zones

• 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)

They’re Pulling Apart!

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

Thingvellir, the spreading zone in Iceland between the North American (left side) and Eurasian (right side) tectonic plates. January 2003.

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

• Plates slide past one another horizontally

Transform Boundary- Plates sliding past one another

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

For example: Here, the San Andreas Fault lies on the boundary between two tectonic plates, the north American Plate and the Pacific Plate. The two plates are sliding past each other at a rate of 5 to 6 centimeters each year. This fault frequently plagues California with earthquakes.

Transform Boundary

Review… Which is what??

DIVERGENT CONVERGENT

TRANSFORM

Force moving Plate tectonics: CONVECTION CURRENTS

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 Layers in the Earth

• Nicolas Steno -was a Danish anatomist and geologist in 1636-1686

• Law of Superposition – says that rock layers on the bottom of sedimentary rock are older than the layers on top.

• That means fossils found in lower layers of rock are older than fossils found closer to the surface.

Rock Layers (strata)

• Which layer of rock would be the oldest?

• A – Closer to the center of the Earth-bottom layer

• Which layer of the rock would be the youngest?

• F – closer to the top (surface)

Rock Layering…

•James Hutton (1729-1797) -Scottish Chemist and Geologist

• The law of cross-cutting – That if there is a faulty or other body of rock that cuts through another rock, then it must be younger in age than the rock through which it cuts into or displaces

Law of Cross- Cutting

• Would Rock D be older or younger than rock A and rock B??

• Younger because it is the rock that CUTS into the rock below!

Fold – bends in the earth’s crust due to stress

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

• Appalachian Mountains ranging from Quebec to Alabama, Rocky Mountains ranging from British Columbia to New Mexico

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.

Whiteboard Practice• Name the 3 layers of the Earth.

• Crust, Mantle, Core

• What is the top layer of the mantle called?

• Asthenosphere

• What is the layer that is the tectonic plates called?

• Lithosphere

Whiteboard Practice• What is the landmass called that was composed of

all the current continents before they drifted apart?• Pangaea• Name the scientist who came up with the theory of

continental drift?• Alfred Wegener• Name proof that Wegener used for his theory of

continental drift.• Fossil’s findings on different continents, Noticed the

continents appear like ‘puzzle pieces’, glacier deposits

Whiteboard Practice• What do Convergent Boundaries create

when it’s two continental plates?

• Mountains!

• What do Convergent Boundaries create when its an oceanic and continental plate?

• Subduction Zone

• What type of boundary created mid-oceanic ridges?

• Divergent

Whiteboard Practice• What type of boundary causes

earthquakes and volcanic activity?

• Transform

• What does a subduction zone cause?

• Oceanic trenches and can help form volcanoes

• What causes tectonic plates to move?

• Convection Currents

Whiteboard Practice

• What theory involves a divergent boundary under the ocean creating new oceanic crust?

• Sea Floor Spreading

• What law says that rock found in lower levels of the Earth are older than rock found towards the surface?

• Law of Superposition

Whiteboard Practice• Name the scientist who came up with the

Law of Superposition.

• Nicolas Steno

• According to the Law of Cross-cutting, which rock layer below would be the youngest?

• Layer D

Whiteboard Practice• What type of rock is made due to bends in

the Earth’s crust from stress?• Folded Rocks• What type of rock is made due to breaks in

the Earth’s crust caused from stress?• Faulted Rocks• What is the areas called where the

majority of the world’s earthquakes and volcanoes occur?

• Ring of Fire

• END OF SLIDES

• MAKE SURE TO STUDY!!