Detailed notes that summarise the Geography IEB syllabus of Endogenic Forces. Included in these notes are important definitions and concepts to learn as well as diagrams that make the section more understandable.
In 1912 Alfred Wegner published his theory on the drifting of continents
• According to him 300 million years ago all the continents were part of a
large continent which he call Pangea.
• The rest of the world was covered by a large ocean which he called
Panthalassa.
• Over time Pangea broke up into the continents as we know them today. His
facts were
1. All the continents t together like a jigsaw puzzle.
2. Fossils on different continents are the same
3. Continuous belts of minerals and rock formations
Wegner had some interesting explanations for why Pangea broke up.
Namely, the gravitational pull of the moon and the different rotation speeds of
the poles and the equator. Understandably, many of the scientists at the time
did not give any credibility to his theory
Modi cations to Wegners Theory
Arthur Holmes in 1944 suggested that convection currents in the mantle are
responsible for the continents moving.
• The interior of the earth is not equally warm and convection currents ow in
the mantle to element these temperature differences.
• When currents close to the earth’s surface move horizontally, they pull the
sima along and the continents drift with it
Alex Du Toit, a South African believed that Pangea rst broke up into a
northern and southern part.
The Northern part: Laurasi
Present day: Europe, North America, Asia
The Southern part: Gondwana Lan
Present day: Africa, Australia, South America, Antarctica, India
He noticed that there were striations (grooves caused by moving ice) over
most of the southern continents.
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, The theory of continental drift was only of cially accepted by the scienti c
world in the early 1960s, due to new technologies and scienti c discoveries
Alfred Wegner is now recognised as the father of the science of plate
tectonics
Plate Tectonics
With sonar, scientists realised that there were ridges in the middle of the
ocean. Paleomagnetism shows
• The sea oor has spread away from the mid ocean ridges
• The continents were once joined as the magnetic alignment matches
Supporting Evidenc
- Similar fossils on the southern continents
- Same ferns found on 5 continents
- Mountain belts are continuous
- The continents t together like a jigsaw puzzl
- Glacial striation
- Younger rocks are found next to the mid ocean ridge due to the sea oor
spreading
- Clear stripes in the magmatism of rock
- Coal deposits found on antarctica showing that it was once found at the
equato
The Theor
The theory of plate tectonics states that the earth has 7 major plates and 12
minor plates. The plates consist of continental masses plus parts of the
adjacent oceanic oor. They oat on part of the outer mantle or
asthenosphere.
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