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Plate Tectonics

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Cassie Henderson-Moulton

on 4 February 2016

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Transcript of Plate Tectonics

Plate Tectonics
Continental Drift
When looking at a map of the Earth there are certain parts that seem to fit together, a lot like puzzle pieces.
seafloor spreading
After World War I, we had new technology that we used to start mapping our seafloors. The first thing we found were underwater mountain ranges (mid-ocean ridges) and no one could explain why they were there. It wasn't until 1960 when scientist Harry Hess suggested seafloor spreading.
The Theory of Plate Tectonics
Combining Wegener's idea of continental drift with Harry Hess' seafloor spreading idea, we discovered the theory of plate tectonics.
Plate Boundaries
At the edges of each plate, there are interactions between them. Usually it's just two plates, sometimes it can be three though. How they move with/against/away from each other depends on what happens at that boundary.
Chapter 10
Alfred Wegener first coined the term continental drift. He proposed that at some point in Earth's past, all of the continents formed one super-continent and slowly moved apart.
Wegener couldn't explain why the continents were moving. He died before most of the scientific community realized that he had been right.
Evidence is in the fossils
There were a few "clues" used to pieced together the information about continental drift:
1. The puzzle-like fit of some of the continents.
2. Fossils of animals found on different continents.
3. Fossils of the same plant found on different continents.
4. Fossils of warm weather plants in cold climates and traces of past glaciers in warm climates.
5. Matching rock compositions on different continents
But Wegener still couldn't explain why the continents were moving!
Hess proposed that hot, dense, mantle rises towards the surface at mid-ocean ridges. The hot molten rock flows sideways and cools when it hits the cold ocean water, carrying the seafloor away from the ridge. (Spreading).
Evidence for Seafloor Spreading
1. Rock samples from both sides of the spreading ridge match.
2. Younger rocks are found right near the ridge and older rocks further away from it.
3. Magnetism, ocean rocks locked in the direction of magnetism (north or south) and that can be used to track the movement of the seafloor.
Earth's crust is made up of sections called plates. Plates are made of crust and the very upper portion of the mantle. We call these two pieces together the lithosphere. Below, in the mantle we call this area the asthenosphere.
1. When plates move away from each other: we call that a divergent plate boundary.

2. When plates move together: we call that a convergent plate boundary.

3. When plates slide past each other: we call that a transform plate boundary.
We still aren't exactly sure what drives plate tectonics, but some ideas are:

1. Convection inside Earth: heat always rises, when it rises it eventually cools and falls back down creating a circular current.

2. Moving convection within the mantle.
Causes of Plate tectonics
Features Caused by Plate Tectonics
Faults are ALWAYS found at plate boundaries. There are two types of faults to know: normal or reverse.
Rift Valleys happen when spreading zones form on the surface of the Earth.
Mountains, islands and volcanoes are frequently associated with plate tectonics.
Read chapter 10.
Page 275: 1-4
Page 278: 1-4
Page 289: 1-4
Pages 294-295: 1-20
Due: 12/16
Full transcript