What is Pangaea?
Pangaea was a supercontinent that existed about 300 million years ago.
All Earth’s continents were joined together before slowly drifting apart.
Continental Drift Theory
Alfred Wegener
In 1912, Wegener proposed that:
- continents were once connected
- they slowly moved over time
- Earth’s surface changes over millions of years
This idea became known as continental drift.
Evidence for Continental Drift
1. Matching Coastlines
South America and Africa appear to fit together like puzzle pieces.
2. Fossil Evidence
The same fossils were found on continents now far apart.
Examples:
- Mesosaurus fossil found in Africa and South America
- Glossopteris plant fossils found across southern continents
This suggests the continents were once joined.
3. Rock and Mountain Evidence
Similar rocks and mountain ranges are found on different continents.
Example:
- Appalachian Mountains (USA)
- Caledonian Mountains (Scotland)
These likely formed together before continents separated.
4. Climate Evidence
Evidence of glaciers was found in places that are now warm.
This suggests continents were once located in different climates.
Why Wegener’s Theory Was Rejected
Scientists originally rejected Wegener’s theory because:
- he could not explain HOW continents moved
- there was no known force strong enough
Later discoveries provided the explanation.
Plate Tectonics Theory
Modern Explanation
Earth’s outer layer is broken into large pieces called tectonic plates.
These plates move slowly over the semi-molten mantle.
Layers of Earth
Crust
Thin outer layer
Mantle
Hot semi-solid rock beneath crust
Core
Very hot centre made mostly of iron and nickel
Plate Movement
Mantle Convection
Heat inside Earth causes mantle material to move slowly.
This movement drags tectonic plates.
Types of Plate Boundaries
Divergent Boundary
Plates move apart.
Results:
- mid-ocean ridges
- volcanoes
- new crust formed
Convergent Boundary
Plates move together.
Results:
- mountains
- volcanoes
- earthquakes
- subduction zones
Transform Boundary
Plates slide past each other.
Results:
- earthquakes
Seafloor Spreading
New ocean crust forms at mid-ocean ridges.
Older crust moves away from the ridge.
This provided strong evidence for plate tectonics.
Key Terms
| Term | Meaning |
|---|---|
| Continental Drift | Movement of continents over time |
| Plate Tectonics | Theory explaining plate movement |
| Pangaea | Ancient supercontinent |
| Fossil | Preserved remains of living things |
| Mantle Convection | Movement of hot rock in mantle |
| Subduction | One plate forced beneath another |
| Lithosphere | Rigid outer layer of Earth |
| Asthenosphere | Soft layer beneath lithosphere |
Important Exam Points
Remember:
- Continental drift was Wegener’s original idea.
- Plate tectonics is the modern accepted theory.
- Evidence is critical in science.
Sample Exam Questions
- Name two pieces of evidence for continental drift.
- Why was Wegener’s theory rejected at first?
- Explain how tectonic plates move.
- Describe what happens at a convergent boundary.
- Explain how fossils support continental drift.
Quick Summary
\text{Pangaea split apart as tectonic plates slowly moved over millions of years.}
- Continents were once joined
- Evidence includes fossils, rocks, climate, and coastline shapes
- Tectonic plates move because of mantle convection
- Plate movement causes earthquakes, volcanoes, and mountains