Plate Tectonics Earth Science Continents

plate tectonics

1. Plate Tectonics and the Continents L8

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3. This Week’s Assignments

4. So…what are we doing

5. Do you know the continents? North America South America Europe Asia Africa Australia Antarctica 1 2 3 4 5 7 6

6. Continental Drift 1912 – Albert Wegener – continental drift hypothesis Supercontinent – Wegener’s proposed single landmass. He said all the continents used to be one big continent. This big continent was called Pangea He thought the supercontinent starting breaking into smaller continents 200 million years ago. He thought mountains like the Andes in South America came from the crust crumpling (like paper) in places

7. Fossil evidence Wegener had a hypothesis that the same kinds of fossils would be found in areas of continents that used to be connected. Fossils of Mesosaurus were found in eastern South America and Western Africa Mesosaurus was small and has been extinct for a long time. So Wegner didn’t think they swam the Atlantic ocean There was no evidence that a land bridge connected both continents mesosaurus

8. Other Evidence The ages of rocks in coastal areas that are far from each other (like western Africa and easters South America) were the same. Another example: The Appalachian Mountains are similar to mountains in Greenland, Scotland, and Europe. Tropical plant fossils were found in areas that now have much colder climates. There are layers of debris from ancient glaciers in Southern Africa and South America

9. Rejecting Wegener’s hypothesis Wegener thought continents moved by plowing through the ocean floor Other scientists rejected this idea. It was easily disproven by geologic evidence. He tried to figure out a better mechanism for the rest of his life but he couldn’t produce anything. The evidence he needed was discovered two decades later

10. Evidence in the OCean 1947 – Scientists map the Mid Atlantic Ridge, part of a system of mid-ocean ridges Mid-ocean ridges : undersea mountain ranges with steep narrow valleys in the middles Sediment on the ocean floor is thinner closer to the ridge than farther from the ridge. The ocean floor is very young. Land rocks are as old as 3.8 billion years. Ocean rocks are at a maximum 190 million years old. Rocks closer to a mid-ocean ridge are younger than those farther from the ridge.

11. Sea floor spreading 1950s Harry Hess – hypothesis – He thought that the valley at the center of a mid-ocean ridge was a crack in the Earth’s crust. Sea-floor spreading: the process where magma rises to the Earth’s crust and cools and solidifies at a mid-ocean ridge If the ocean floor was moving, he thought the continents might be moving too.

12. paleomagnetism Paleomagnetism: the study of the magnetic properties of rocks. When magma cools and solidifies at mid ocean ridges, the magnetic iron in the molten rock turns to align with the magnetic field of the Earth. Sometimes, the Earth’s field turns around, so some of the rocks near a ridge have their magnetic poles reversed. This helps scientists figure out the ages of rocks

13. How does Magnetism work?

14. Magnetism Imagine every magnet as a bunch of small magnets. A rock or piece of metal can be magnetic if all the little magnets point in the same direction. In the hot magma in a min-ocean ridge, the little magnets can move.

15. Plate tectonics Theory of Plate Tectonics: a theory that explains why and how the continents move. Tectonic plates: the blocks that make up the Lithosphere. They ride on the Asthenosphere. There are 15 tectonic plates

16. The Tectonic Plates

17. The plates Continent boundaries don’t always match the plates Plate boundaries can be found by studying earthquakes Earthquake : movement of the Earth caused by a release of energy when rocks move along a fault line Fault line : A break in the tectonic plates where they slide along each other.

18. Plate tectonics video https://www.youtube.com/watch?v=ryrXAGY1dmE

19. How will earth look https://www.youtube.com/watch?v=hos7w8xrcEs

20. Pangea video https://www.youtube.com/watch?v=q-ng6YpxHxU