Convection currents in mantle driven by heat from earth’s core
Fig. 6 Exam Diagram: The tectonic cycle: the continuous destruction and formation of the earth’s crust at plate boundaries.
Development of the theory of plate tectonics Continental drift – Wegener 1912
The basis for modern plate tectonic theory was proposed by Alfred Wegener in 1912. Wegener believed the earth was once one large landmass which he called Pangaea (all land). He stated that Pangaea split into two large continents called Gondwanaland and Laurasia. With time these then split into the landmasses and oceans we see today. He called this continental drift.
Wegener based his theory on the evidence listed below: 1. The distribution of identical fossils around the world.
2. Matching mountain trends and rock types on continents separated by thousands of miles of sea (Scandinavia
Appalachians in the USA).
3. Matching coastline shape (Africa and South America).
At first most scientists did not accept Wegener’s
theory
because he could not explain how the continents moved. He was convinced, however, and continued to collect data in support of his ideas. He died while on expedition in Greenland trying to prove his theory. Today the idea of continents moving around is widely accepted.
Cynognathus 3m long
Glosopteris
Mesosaurus (freshwater)
Lystrosaurus
Fig. 7 Distribution of fossils across the southern continents of Pangaea 5