Theory Of Continental Drift Alfred Wegener It is this German man to whom we credit with the proposal...
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Transcript of Theory Of Continental Drift Alfred Wegener It is this German man to whom we credit with the proposal...
Theory Of Continental Drift
• Alfred Wegener
• It is this German man to whom we credit with the proposal of the theory of Continental Drift.
• While pondering the similarities between the coastlines of South America and Africa, Wegener came up with an idea:
• What if the continents were once all connected and just drifted over the years?
Wegner’s evidence for Continental drift
• Ferns and Reptiles in many different continents
• Glaciers that were then tropical forests
• Same types of rocks on continents close to each other (yet separated by an ocean)
• The coastlines of Africa and South America
The Flaw in Wegner’s Theory
• He thought that each of the continents were a separate plate--they were just drifting on a never-changing ocean.
• Like styro-foam floating on a pool of water!!
Canadian Correction
• J. Tuzo Wilson
• the 1960’s Canadian scientist who resurrected Wegner’s theory after years of disbelief by the science community.
• Today, we know that that's false, thanks to the discovery of crustal plates.
• The plates of the earth are not composed of just land; they're composed of ocean too.
Canadian Correction – cont’d
• In some cases, the plates are just land, in others they're just ocean, and, in still other cases, they consist of land and ocean.
• They each have different boundaries and move in all different directions.
Continental Drift
• refers to the movement of the more than 20 plates (9 major) due to convergent, divergent, and transform boundaries.
• The continents drift at a rate of 2 inches a year.
• Started 200 million years ago
• Pangea (land) & Panthalasa (sea)
More about Continental Drift
• our text p. 10
• watch it at:
• http://www.ucmp.berkeley.edu/geology/tectonics.html
Plate Tectonics
• Tectonic plates move or float on top of the upper mantle.
• However they do not float freely.
• The plates are forced in specific directions by the flow of magma beneath.
Plate Tectonics – cont’d
• Plates move with the flow of magma.
• The magma closer to the core heats and then rises towards the surface as its density decreases.
• Once the rising magma reaches the lithosphere it moves in opposite directions.
• The magma forms convectional currents.
Divergent Boundaries
• Tensional Forces occur where two tectonic plates are pushed apart. The tension is created as the plates move away from each other.
• Ridge Zones sometimes occur where two plates move apart. The magma rises between the plates and forms a ridge.
• Again caused by convectional currents in the magma
Convergent Boundaries
• Compressional Forces occur where two tectonic plates come together. They compress against each other.
• Subduction Zones sometimes occur where compressional forces result from two plates colliding and one plate slips under the other.
• Again caused by convectional currents in the magma
More about Plate Tectonics
• our text p. 10 - 12
• watch it at: • http://
www.pbs.org/wgbh/aso/tryit/tectonics/intro.html