plate tectonics continental drift theory theory of plate tectonics plate boundaries

Plate Tectonics•Continental Drift Theory•Theory of Plate Tectonics•Plate Boundaries

Plate Tectonics - Continental Drift

Definition: Continental Drift

• It is the theory that the earth’s continents are constantly in motion and at one time they all collided together to form one massive continent about 300 million years ago!

• Pangaea (meaning “all lands”) began to break up and drift apart.

Founder of the Continental Drift Theory

• Alfred Wegener came up with the idea in the early 1900’s.

• He believed that the world shared certain characteristics that proved that at one time the continents were all together.

Plate Tectonics - Continental Drift

Proof # 1

• Visually, he saw that the continents of Africa and South America would fit together like a jigsaw puzzle.

Proof # 2

• There were fossils of animals and plants on both continents!

Proof # 3

• There are mountain ranges and structures on different continents that could be lined up if they were one large continent.

• For example: Appalachian and Caledonian Mountains

Proof # 4

• There is proof that ice sheets had once covered the southern portions of South America, Australia, India and Africa – how could this happen in places that are so warm today? Glaciers could have only formed if the continents were close to the south pole.

• However, the theory was debated because scientists wanted evidence to explain how the continents could drift across the earth’s surface.

…thus the theory of PLATE TECTONICS (1960s)

•Theory of Plate Tectonics offered a more scientifically sound explanation for the movement of continents.•Plate Tectonics is the movement of the earth’s surface (crust) which is divided into 6 major plates. Within each major plate, there are numerous sub-plates as well.

•Large convection currents in the mantle cause plates to move.•The mantle lies under the crust.•Earth radiates huge amounts of energy from the radioactive decay of elements in the core.This energy makes its way outwards through the mantle toward the crust•This heat gives the mantle “plastic” characteristics, which means that it is very slowly moving with giant convection cells that carry the heat to the Earth’s surface.

•Plate boundaries occur when 2 or more plates meet each other. There are 4 types of plate boundaries.

Plate Tectonics Map

Plate Tectonics Processes

Notice that the trench is parallel to the shoreline and

the mountain range

1. Divergent

• Found in the middle of the Atlantic Ocean (mid-Atlantic Ridge) .

• New land is created by volcanic activity.

1. Divergent

•The Mid-Atlantic Ridge is a divergent boundary.

2. Convergent

• Found in the Himalayas.

• Fold mountains and trenches are created.

2. Convergent

2. Convergent

3. Subduction

• Takes place at convergent boundaries.

• One plate moves underneath the other plate.

• Found on Canada’s West Coast.

• Volcanoes are produced along with earthquakes at great depths.

3. Subduction - Volcanoes

• The plate moving deeper into the earth melts due to the hot temperature, melting the earth’s crust into liquid form called molten.

• The molten finds a hole in the ground and builds up creating a volcano. Molten inside the volcano is called magma. When the volcano explodes due to gas build up (hot temperatures), magma becomes lava. Lava cools and turns into rock on the earth’s surface.

3. Subduction

3. Subduction - Volcanoes

4. Transform

• Found in California (San Andreas Fault).

• Earthquakes are produced.

4. TransformEarthquake in Kobe, Japan

4. TransformEarthquake in Kobe, Japan

4. Transform

4. Transform

Tectonic setting of western British Columbia and Washington state. The oceanic Juan de Fuca plate is moving beneath the continental North America plate at a rate of

about 4 cm/year. Great earthquakes occur along part of the boundary between the two plates.

4. Transform - Earthquakes

Richter Scale – measures the magnitude of earthquakes

• Less than 3.5 Generally not felt, but recorded.• 3.5-5.4 Often felt, but rarely causes damage.• Under 6.0 At most slight damage to well-

designed buildings.• 6.1-6.9 Can be destructive in areas up to about

100 kilometres across.• 7.0-7.9 Major earthquake. Can cause serious

damage over larger areas.• 8 or greater Great earthquake. Can cause serious

damage in areas several hundred kilometers across.

Ring of Fire

• ↑ in tectonic plate activity

• 75% World’s active volcanoes

• 90% World’s earthquakes; 80% World’s largest earthquakes