The Earth's surface is very ____ - lots of ____ and ____
The Earth's surface is very crinkly - lots of mountains and valleys
What did scientists previously think caused the Earth's 'wrinkled' surface?
The shrinkage of the surface as it cooled down after the Earth was formed
What replaced the theory of surface shrinkage?
Who came up with the theory of continental drift?
What were the 2 main pieces of evidence that pointed to Wegner's theory of continental drift?
1. Similar organisms' fossils found on opposite sides of the Atlantic ocean
2. The sides of continents 'matching up' in shape and layer
3. Fossils found in 'wrong' places
How did fossil findings help Wegner come up with the theory of continental drift?
1. Came across some work listing the fossils of very similiar plants and animals which had been found on opposite sides of the Atlantic ocean
2. Investigating further, he found other cases of this.
How did other scientists explain the discovery of fossils of very similar organisms found on opposite sides of the Atlantic ocean?
That there had once been land bridges connecting the continents which animals could cross.
Believed they had 'sunk' or been covered over since then
Describe Wegner's 2 findings of 'matching' continents
1. The coastlines of Africa and South America seemed to 'match' like pieces of a jigsaw
2. There were matching layers in the rocks in different continents
What was Wegner's thinking behind the 'matching' of the coastlines of Africa and South America?
Wondered if they had previously been one continent and then split
Give an example of fossils being found in the 'wrong' places
Fossils of tropical plants being found on Arctic islands, where the current climate would clearly have killed them off
When did Wegener publish his theory of continental drift?
Describe Wegner's theory of continental drift
About 300 million years ago there had been just one supercontinent called Pangaea.
It broke into smaller parts which moved apart.
These parts - our modern-day continents - are still drifting apart
Was Wegner's theory accepted straightaway?
It took many years to convince people
How did the majority of other scienists react to Wegner's theory?
They reacted with hostility
What were the 4 main reasons scientists at the time opposed Wegner's theory?
1. Wegner said continents were 'ploughing through' the sea bed, and their movement was caused by tidal forces and the Earth's rotation
- other geologists said this was impossible - 1 said it would stop the Earth's rotation (which it hadn't)
2. Wegner had used innacurate data - wild predictions about speed of continental drift
3. Wegner was an astonomist, not a 'proper' geologist
4. Wegner was quite young - seen as inexperienced and not respected
What happened in the 1950s concerning continental drift?
In an investigation of the ocean floor, new evidence found to support it.
Main idea = correct
When was the theory of continental drift accepted as the main theory?
In the 1960s
What is our belief concerning continental drift today?
The Earth's crust is made up of several parts called tectonic plates which move around, and that colliding plates push the land up to create mountains