3. Matching rocks and mountain ranges: The mountain ranges of the east coast of the USA (e.g. Appalachian mountains) and north-western Europe (i.e. Connacht, Ulster, Scotland and Scandinavia) have similar features and are more than likely related. Formed during the Caledonian mountain building period, these mountain ranges have a similar rock type (granite) and directional trend (south-west to north- east).
4. Ice sheets once covered areas that today are very warm: Places such as India, Australia and South Africa couldn’t support an Ice Age based on their current latitude. Lying close to the equator, the remains of the ice sheets found here suggest that these areas once existed at different latitudes before being moved by continental drift.
Freshwater reptiles cannot survive in saltwater environments such as oceans.
Fig. 1.2 Wegener’s theory of continental drift. CHECK YOUR LEARNING
1. What are endogenic forces? 2. Which layer of the earth is the hottest? 3. Suggest one reason why this layer is the hottest. 4. Which layer of the earth is the thickest? 5. Who proposed the theory of continental drift?
Sea-Floor Spreading
Most scientists only accepted Wegener’s continental drift theory after Harry Hess discovered sea-floor spreading at the Mid-Atlantic Ridge. In 1960, Hess, a professor at Princeton University in the United States, noticed that:
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the age of the rock on the sea floor is youngest along mid-ocean ridges;
rocks get progressively older and deeper the further one moves from this point (Fig. 1.3).
6. What do the abbreviations SIMA and SIAL stand for?
7. What was Pangaea? 8. Explain two pieces of evidence that back up the theory of continental drift.
Europe Europe
Africa Africa
Australia Australia
Antarctica Antarctica
Asia Asia
Oldest rock
Youngest rock Mid-Atlantic Ridge
Oldest rock
NORTH AMERICA
Ocean floor
Convection currents
Mantle Magma
Fig. 1.3 Sea-floor spreading – crust gets progressively older moving away from the mid-ocean ridge.
