Plate Tectonics
Alfred Wegners Theory Came up with the the Theory Continental Drift and said that there are several pieces of evidence that support it.
The Theory of Continental drift All continents were once connected as one large landmass called Pangaea. Landmass broke apart and drifted to their present positions.
Pangea Pangea was the ancient Supercontinent that existed when all of the continents were connected. If you look at a map of the continents they seem to fit together like a jig saw puzzle
Puzzle like Fit
Animal Fossils Fossils of a freshwater reptile, Mesosaurus, were found on South America and Africa. Mesosaurus could not have swam over the Atlantic Ocean.
Plant Fossils Fossils of the plant, Glossopteris, were found in Africa, India, South America, and Antarctica which all have different climates.
Glacial Deposits Eroded rocks and debris left behind by ancient glaciers can be found in South America, Africa, India, and Australia which all have different climates and are not near the poles.
Similar Rock Structures Rock formations identical to the American Appalachian Mountains can be found in Greenland and Western Europe
The Theory of Seafloor Spreading On the ocean floor there are areas where the seafloor is getting bigger. Researchers used sound waves to discover a system of underwater ridges or mountains that can be found all over the world.
Mid Atlantic Ridge This underwater chain of mountains and volcanoes is found in the middle of the Atlantic Ocean. http://www.youtube.com/watch?v=DWKWdfJtNl0 http://www.youtube.com/watch?v=6CsTTmvX6mc
Why does the Seafloor Spread? Hot, Less dense material below Earth’s crust rises upward to the surfaces at the mid ocean ridges. Then, it, flows sideways, carrying the seafloor away from the ridge. As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.
Evidence for Seafloor Spreading Youngest rocks are located at mid-ocean ridges.
Evidence for Seafloor Spreading Reversal of Earth’s magnetic field are recorded by rocks in strips parallel to ridges. These iron rich rocks point towards magnetic North wherever it is at the time they cool.
Discussion Question How could seafloor spreading be related to continental drift?
Answer If the Seafloor is constantly spreading apart and moving, it will effect and move the continents as well.
Theory of Plate Tectonics Earth’s crust and upper mantle are broken into sections called plates, they move on a plastic-like layer of the mantle. Plates and upper mantle form the lithosphere. Plastic-like layer below is called asthenosphere.
Types Plate Boundaries Divergent Plate boundaries Plates moving apart causing ridges and rifts
Divergent Plate Boundaries
Plates Collide Convergent Boundaries Plates moving together. Denser plates sink under less dense plates. Newly formed hot magma forced upward forms volcanic mountains
Plates collide Plates crumple up to form mountain ranges. Earthquakes are common
More Plate boundaries Transform boundary Plates slide past one another. Sudden movement can cause earthquakes Ex. San Andreas Fault in California
Convection Current Hot, less dense melted rock in the earths mantle rises and sinks in a circular motion causing the plates to move and magma to rise. This is the driving force behind Plate Tectonics, Seafloor Spreading and Continental Drift.
Convection Currents: the cause of plate tectonics