ZIMSEC O Level Geography Notes: The theory of continental drift
- The theory of or idea that present day continents were once one single continent.
- Continental drifts refers to the movement of continents.
- The theory says that continents have been moving for millions of years and still do so today.
- According to theory about 180 million years ago there was only one super continent which was the sole major landmass called Pangea
- This later broke into two pieces a northern block called:
- Laurasia which divided further and from which later came most of present day North America and Europe) and the southern part called
- Gondwanaland which further divided and from which came the continents of South America, Africa, the Sub-continent and Australia).
- The sub-division of these two major landmasses happened about 65 million years ago resulting in the formation of present day continents.
Evidence of continental drift.
- Several pieces of evidence have been put forth to justify the theory:
- The jig saw shape of continents. When viewed by satellites and on maps, the appearance of continents gives the impression that if they were pushed against each other like pieces of a jig saw they would fit. For example South America would fit into West Africa and Australia into East Africa and Asia. This seems to suggest that these continents were part of one big continent.
- Geological evidence shows that there are similarities between rocks on the west coast of Africa and those on the east coast of South America.
- Flaura and fauna-animals and plants of Australia, South America and West coast of Africa suggest that they were one continent.
- Paleo magnetism evidence -this is an advanced scientific method of determining the age of rocks. Rocks are magnetized in the direction of compass north when they solidify. By studying the age of rocks scientist have been able to tell the position, relative to the earth’s surface when they were formed. This is the greatest single piece of evidence that shows the earth has moved.
Why the theory was initially rejected
- It did not explain why the continents moved nor did it give the cause/force that caused the continents to move.
- The early claims of the distance traveled by the continents were high ( 250cm/year) it has been shown the continent of Africa moves at about 2.5cm/ year.
The claim made in some texts that the earth is no longer moving are simply untrue and the student should ignore these.
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