1.2 Outline Plate Tectonics
Alfred Wegner—Proposed:
A. Continental Drift
1. Pangaea
2. Hypothesis proposed by
B. Pangaea
1. Large super
C. Evidence for continental drift
1. Fossils
2. Rock formations (layer sequence)
D. Wegner’s hypothesis was not accepted because:
Seafloor spreading – Theory proposed to explain
1.
2.
3.
4.
Mapping of the sea floor showed underwater mountain ranges Mid-ocean ridges and trenches
Magma rises up from mantle
The new crust pushes the old crust away
This explained how the crust could move
Evidence for seafloor spreading
1. Rock samples showed that the youngest rock is closest to the ridge and the older rock is farther
away
Mechanism for plate movement (Causes of Plate movement)
1. Convection Currents
a. Soft hot rock rises, cools and sinks then is heated and rises again
b. Flows in a continuous loop
2. New land is formed at the ridge pushing the plates apart Ridge Push
3. Land is gobbled up, pushed down at the subduction zone Slab Pull
Theory of Plate Tectonics
1. The Earth’s lithosphere (crust and upper mantle) are made up of plates that move on the mantle
2. Plates move apart, push together, or scrape past each other causing changes
a. Earthquakes
b. Volcanoes
c. Mountain ranges