Pangaea
Pangaea was a supercontinent where all Earth’s continents were joined together about 300 million years ago.
Over millions of years, Pangaea broke apart and the continents moved into their current positions.
Breakup of Pangaea
Laurasia
Northern supercontinent:
- North America
- Europe
- Asia
Gondwana
Southern supercontinent:
- Australia
- Antarctica
- Africa
- South America
- India
Australia was once connected to Antarctica as part of Gondwana.
Alfred Wegener
Wegener proposed the theory of continental drift in 1912.
He suggested:
- continents move slowly over time
- continents were once joined together
Scientists rejected the theory at first because Wegener could not explain how continents moved.
Evidence for Continental Drift
| Evidence | Explanation |
|---|---|
| Matching coastlines | Continents fit together like puzzle pieces |
| Fossils | Same fossils found on separate continents |
| Rocks & mountains | Similar geology across continents |
| Climate evidence | Glacial evidence found in warm regions |
Examples of fossils:
- Mesosaurus
- Glossopteris
Plate Tectonics Theory
Modern theory explaining continental movement.
Earth’s outer layer is broken into tectonic plates that move slowly over the mantle.
Structure of Earth
| Layer | Description |
|---|---|
| Crust | Thin outer layer |
| Mantle | Hot semi-solid rock |
| Outer Core | Liquid iron and nickel |
| Inner Core | Solid iron and nickel |
Mantle Convection
Heat from inside Earth causes convection currents in the mantle.
These currents slowly move tectonic plates.
\text{Heat inside Earth causes mantle convection, which moves tectonic plates.}
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
Earthquakes
Earthquakes occur when tectonic plates suddenly move along faults.
Important terms:
- Focus (hypocentre): underground starting point
- Epicentre: point on Earth’s surface above the focus
Earthquakes release seismic waves.
Volcanoes
Volcanoes form when magma rises through Earth’s crust.
Magma
Molten rock underground
Lava
Molten rock on Earth’s surface
Volcanoes commonly occur near plate boundaries.
Seafloor Spreading
New ocean crust forms at mid-ocean ridges.
Older crust moves away from the ridge.
This provided strong evidence for plate tectonics.
Natural Hazards
Plate movement can cause:
- earthquakes
- volcanoes
- tsunamis
Scientists study tectonic activity to reduce risk and improve preparedness.
Geological Time
Earth is about 4.5 billion years old.
Geological changes happen slowly over millions of years.
Key Terms
| Term | Meaning |
|---|---|
| Continental Drift | Continents moving over time |
| Plate Tectonics | Theory explaining plate movement |
| Pangaea | Ancient supercontinent |
| Gondwana | Southern supercontinent |
| Laurasia | Northern supercontinent |
| Mantle Convection | Movement of hot mantle rock |
| Subduction | One plate forced under another |
| Epicentre | Surface point above earthquake focus |
| Lithosphere | Rigid outer layer of Earth |
Common Exam Questions
- Describe two pieces of evidence for continental drift.
- Why was Wegener’s theory rejected?
- Explain mantle convection.
- Compare the three plate boundaries.
- Explain how earthquakes occur.
- Describe how seafloor spreading supports plate tectonics.
Quick Summary
\text{Pangaea split apart as tectonic plates slowly moved due to mantle convection inside Earth.}
- Continents were once joined together
- Evidence includes fossils, rocks, coastlines, and climate
- Tectonic plates move slowly over time
- Plate movement causes earthquakes, volcanoes, and mountains
- Plate tectonics is the accepted modern theory