What is the Theory of Continental Drift?�

• The current continents were once connected into a supercontinent and have since broken apart and drifted to their current positions.
• This theory was developed by Alfred Wegner.
• He named the supercontinent Pangaea

PANGAEA -- Greek meaning “all lands”

Stretched from pole to pole and centered where Africa is today

Evidence Supporting Continental Drift

Continental Coastlines Evidence

• The coast of different continents are similar (especially the east coast of South America and the west coast of Africa).

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Evidence Supporting Continental Drift

Fossil Evidence

• Fossils of the same organisms are found on different continents.

Evidence Supporting Continental Drift

Landform Evidence

• Similar rock formations found on different continents. When lined up, they are the same type of rock and age.
• Coal deposits found on different continents. When lined up, they are the same type and age.

Evidence Supporting Continental Drift

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Climate Evidence

• Evidence of past tropical climates in the Antarctic.
• Fossils of Glossopteris, a fern-like tropical plant found in colder areas
• Arctic climates (glacier marks) in the tropics.

Continental Drift

Why was the theory of Continental Drift not widely accepted?

He could not provide the force that caused the continents to move.

They felt it would have been impossible for huge solid chunks of land to have plowed through the ocean floor.

What is the Theory of Plate Tectonics?

• It states that the Earth’s lithosphere is broken into pieces called plates which are in constant slow motion; driven by convection currents in the asthenosphere.

• Plates are the broken pieces of the lithosphere.

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• The edges of these pieces are called boundaries .

What are plates & plate boundaries?

How do the plates of the lithosphere affect each other at these boundaries?

• They grind past each other - Transform
• They can pull away from each other - Divergent
• They can crash into each other - Convergent

Transform plate boundary

• A place where two plates grind past each other, moving in horizontal opposite directions.
• Crust is neither created (cooled magma) nor destroyed (melted)

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What are major feature formed by transform boundaries?

• Most transform boundaries connect sections of ridges under the ocean
• Responsible for creating strike-slip faults which lead to strong earthquakes.

Example: San Andreas Fault

Transform Fault Boundary

San Andreas Fault

Divergent plate boundary

A place where two

plates move apart or

Divide.

• Mid-Ocean Ridge
• Forms under oceans
• Chain of erupting volcanoes.

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Example: Mid-Atlantic Ridge

What geologic features form at divergent plate boundaries?

• Rift Valleys
• Forms on land
• Also erupt lava

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Example:

Great Rift Valley in East Africa

What geologic features form at divergent plate boundaries?

East African Rift Valley

Describe a convergent plate boundary.

• A place where two plates come together.
• Collisions occur between:
• Oceanic crust & continental crust
• Oceanic crust & oceanic crust
• Continental crust & continental crust

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What geologic features

form at convergent

plate boundaries when…

Collision between oceanic crust & continental crust

• Form deep ocean trenches
• The oceanic crust is more dense than continental crust so it sinks or SUBDUCTS under the continental forming a deep-ocean trench.
• Form volcanoes on continental crust
• The subducting plate melts, the melted rock is less dense and rises to create volcanoes

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Examples: Andes & Cascadian Mountains

DEEP-OCEAN TRENCH

Subduction

&

Volcanic eruption

oceanic crust & oceanic crust

• Form deep ocean trenches
• Form arc islands (volcanic)

Examples: Japan & Aleutian Islands

Collisions occurring between �continental crust & continental crust

• form mountain ranges

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Example: Himalayan Mountains

Continental crust & continental crust

Collision of India and Asia

YouTube:

Mt Everest

Animation