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Lesson 4
Alfred Wegener
Learning Outcomes:
• You will be successful if you can:
• Describe the evidence for the movement of continents.
• Explain why Wegener’s ideas were rejected by his peers.
• Remember that Scientists may agree on data but argue about meanings.
How do mountains form?
Theory 1: Cooling, contracting-Earth theory.
Mountains formed on the Earth's crust as wrinkles form on the skin of a drying apple.
But why are they not evenly spread?
Surely the earth would have cooled down by now?
People once thought that the oceans and the continents were formed by shrinkage from when the Earth cooled down after being formed.
Alfred Wegener proposed something different. Consider Africa and South America:
Tectonic theory
These continents look like they “fit”
together. They also have similar rock
patterns and fossil records. These two
pieces of evidence led me to believe that there was once a single land mass.
This is my TECTONIC THEORY.
Fossil Glossopteris leaf
Glaciation
300-180mya
Theory 2: Continental drift.
Mountains formed when the edge of a drifting continent pushed into another, causing crumpling and folding. But isn’t the Earth made of solid rock?
Wegener also noted that when you fit Africa and South America together, mountain ranges (and coal deposits) run uninterrupted across both continents.
Wegener• His ideas were rejected by many geologists.
Some of the reasons for this were:
1. The movement of continents could not be detected.
2. No-one could provide a good explanation of how whole continents could move apart.
3. Wegener was not a geologist (he trained as an astronomer and meteorologist).
4. There were other, simpler, explanations for the same evidence.
5. It was felt his idea was too big for the evidence at hand.
The Evidence:
1) Some continents look like they used to “fit” together
2) Similar rock patterns and fossil records
The Answer:
1) Scientists discovered 50 years later that the Earth generates massive amounts of heat through radioactive decay in the core. This heat generated convection currents in the mantle causing the crust to move
2) We also now know that the sea floor is spreading outwards from plate boundaries
Tectonic theory
The Problems:
Wegener couldn't explain how continental drift happened so nobody believed him
Conclusion – scientists now believe Wegener’s Tectonic Theory
1. Vine says it is significant that Wegener was a ‘meteorologist’ rather than a ‘geologist’.
a What is a ‘meteorologist’?b Discussing reasons for the rejection of the idea of
continental drift, Vine mentions the fact that Wegener was a meteorologist, surveyor, & polar explorer. Why does Vine suggest this is relevant?
2 Why does Vine think Wegener made a mistake by trying to measure the rate of continental drift?
3 Why did most geologists believe Harold Jeffries when, in 1929, he said continents cannot move?
4 Why did the publication of Holmes’s textbook Principles of Physical Geography in 1944 have greater effect than the article he published in The Transactions?
• What was Wegener's evidence? (fossils/rock pattern)
• Why did other scientists not agree with Wegener? (hard to see continents moving/what force could move so much land)
• How could we get the evidence today? (satellite measurement -e.g. GPS)
Answer these questions in your book:
• What was Wegener's evidence? (fossils/rock pattern)
• Why did other scientists not agree with Wegener? (hard to see continents moving/what force could move so much land)
• How could we get the evidence today? (satellite measurement -e.g. GPS)
Answer these questions in your book:
