Theory of _________________

1. Theory of _________________ Plate Tectonics

2. Wegener’s Continental Drift Theory • The continents were not always where they are today but rather have drifted apart over millions of years

3. Evidence • Evidence for Continental Drift Theory includes: • Jigsaw puzzle fit of continent, • Geological structures • Fossils • Climatic evidence • BUT...Wegner was ridiculed • How could entire continents move?

4. More Evidence • In 1915 there was not enough Scientific Evidence for people to believe Wegner’s Theory of Continental Drift • In order for Wegner’s hypothesis to become a theory, he needed to be able to explain HOW or WHAT could make the continents move

5. Today’s Objectives • Be able to define tectonic plates • Be able to list and discuss evidence for tectonic plate movement • Sea Floor Spreading • Hot Spots • Be able to state the Plate Tectonic Theory • be able to explain how the Plate Tectonic Theory helped to silence Wegener’s critics

6. Plate Tectonics • In Wegner’s time, scientists did not know that Earth’s surface was broken up into large, moveable slabs of rock • These slabs are called TECTONIC PLATES

7. Plate Tectonics • These rigid, solid plates float on top of a layer of molten rock • The movement of these plates result in the movement of the continents

8. How do we know the Plates are Moving? There are 4 main pieces of evidence: • Existence and patterns of Earthquakes and Volcanoes • Existence of ocean ridges • Paleomagnetism, the existence of magnetic striping • Existence of volcanic island chains

9. #1: Earthquakes and Volcanoes • occur at plate boundaries (the edges of plates) • appear to occur when adjacent plates collide • stationary objects can not collide • suggests that plates must be moving!!!

10. #2: Ocean Ridges • These are under water mountain ranges • A well known example is the MID-ATLANTIC RIDGE which runs north to south down the entire length of the Atlantic Ocean.

11. Proof??? • Can be best explained as a formation made by two plates moving AWAY from one another • As the plates move apart, they form a gap • The hot magma rises through the gap, cools and forms new rocks/mountains

12. Ocean Ridges

13. Paleomagnetism • This is the study of the magnetic properties of ancient rocks • Like Earth itself, its magnetic field is continually changing • In the last 10 million years the poles have shifted 4-5 times per million years!

14. #3- Magnetic Striping • Scientists have discovered that Iron grains in rocks align with the magnetic poles • They call this pattern MAGNETIC STRIPPING • Stripes of rock at the bottom of the ocean that have alternating magnetic patterns

15. More on Magnetic Striping • Can be explained if the plates are moving apart as the Earth’s magnetic field is reversing oldest rock youngest rock 2nd youngest rock older rock

16. Seafloor Spreading • Ocean ridges and magnetic striping both suggest that the sea floor is spreading or moving • In other words “the plates” are moving

17. #4- Volcanic Island Chains • Are chains of islands that are formed when magma reaches the Earth’s surface and cools

18. HOT SPOTS • hotspots = an area where molten rock rises through the Earth’s surface, cools and forms new rock • Volcanic Island Chains can be explained by Hot Spots • Hot spots are stationary spots located BELOW the tectonic plates • Hot Spots do not move, rather the plates move over the hot spots!

19. As the plates moves, the islands move as well. • As a new portion of the plate moves over the hot spot a new island forms until eventually you get a chain of islands

20. For example, the Hawaiian Islands • They formed when the Pacific Plate moves North East over a hot spot

21. typically the smaller islands = the older island • Why??? • As time goes by the islands get eroded away by the ocean water

22. Plate Direction • Not only does the existence of Volcanic chains and hot spots prove that plates are moving... • They can show the DIRECTION of plate movement!

23. DIRECTION 1-Oldest 2 3 4- Youngest

24. Summary of Evidence that Prove that Plates can MOVE • Earthquakes and Volcanoes = occur as plates move and collide • Ocean Ridges = form as plates move apart • Magnetic Stripes = form as plates move apart • Island Chains = form as plates move over hot spots

25. The Theory of Plate Tectonics • Is a unified theory that came out of the above evidence • States that the Earth’s surface is made up of large plates of rock that float and continually move on top of a molten layer. • Came about after Wegener’s Continental Drift Theory • Supported Wegener’s theory as it explained how continents could move Finally his critics could be Silenced!

26. PLATE FACTS • There are 7 major plates and 5 minor plates – 12 plates total. • It is on the edgesof the plates – near the borders of plates where all the action is! (earthquakes, volcanoes, mountain building!) • These tectonic plates move approximately 1 inch per year due to CONTINENTAL DRIFT!!! • That is the same rate as your fingernails grow!!!

28. What makes the plates move? • We know that the continents drift • We know that they sit of rock slabs called Tectonic Plates • BUT, what makes the plates move and how does it work...