PLATE TECTONICS

Plate Tectonics definitions Plate tectonics – the movement of Earth’s plates on its crust. Continental Drift – the apparent drifting of the continents around the Earth. construction_blakey.html construction_blakey.html Earth’s surface is divided into about 12 major tectonic plates and quite a few minor tectonic plates. te_layers_bath.html te_layers_bath.html Can you find the North American plate? gins.html gins.html

Plate movement The tectonic plates are moved by convection currents inside the Earth. Remember: hot rises and cold sink! Continental Drift – the apparent drifting of the continents around the earth.

Convection current The heat rises from the center of the Earth and pushes on the tectonic plates, moving the plates.

Lithosphere and Asthenosphere The lithosphere is the part of the earth that is moved. It is made up of the crust and the upper mantle. The asthenosphere is where the convection currents are occurring. It is below the lithosphere.

Evidence for Plate Tectonics Scientists use the following to help prove plate tectonics 1. Fossil locations 2. Shape of continents 3. Earthquakes and Volcanoes 4. Magnetism

Fossil Locations One example - Mesosaurus Fossils are found on specific locations on the east coast of South America and the West Coast of Africa. The shape of the continents seem to look like big puzzle pieces. Puzzle

Earthquakes and Volcanoes Most earthquakes and volcanoes happen along plate boundaries

Earth’s magnetic poles switch location. This magnetism can be found by studying rock records. (basalt - contains iron) Magnetism Isochron – a line on a map that connects points that have the same age.

Alfred Wegener – Continental Drift Alfred Wegener first proposed the theory of plate tectonics. He “reversed” time and matched up all the continents shape to create a supercontinent, Pangaea. When he did this, the evidence proved plate tectonics to be accurate. Most rejected his theory at the time because he couldn’t explain what forces could move continents and how continents could move without shattering.

PLATE BOUNDARIES

Plate Boundaries The locations where tectonic plates meet are called plate boundaries. There are 4 kinds of plate boundaries 1 Diverging boundaries – oceanic and continental 2 Converging subduction boundaries 3 Converging collision boundaries 4 Transform boundaries

Diverging ocean boundaries Occur when oceanic tectonic plates are sliding apart. Forms mid-ocean ridges. Evidence in magnetism and age of ocean floor.

Diverging continental boundaries Occur when continental tectonic plates are moving apart. Form rift valley – African Rift Valley

Converging subduction boundaries When one plate slides under the other plate 2 types: Oceanic – Continental Oceanic - Oceanic Results in deep trenches and volcanoes Oceanic – Oceanic Convergence

Why does the oceanic plate slide under the continental plate??? Continental lithosphere is made of relatively light- weight minerals, so it has a low density. Oceanic lithosphere is more dense than continental lithosphere because it is composed of heavier minerals. (basalt)

Converging Collision boundaries Occur when two continental plates crash into each other. (equal densities) Create huge mountain ranges (Himalayas)

Transform Boundaries Also called Sliding Boundaries Occur when one plate boundaries slides past the other Often generates lots of earthquakes Ex: California

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