Unit 5 Quiz 2

1. Unit 5 Quiz 2 Plate Tectonics Online Earth Science Text Chapter 5 Unit 5 Handouts #’s 4-8

2. Layers of earth Pgs. 354-355 in Blue book Crust Lithosphere Asthenosphere Mantle Core

3. Crust • Layer of rock that forms Earth’s outer skin • Includes soil, water, mountains, and rocks • Ranges from 5-40 km thick • Thinnest under ocean (oceanic crust) • Thickest under mountains (continental crust)

4. Mantle • Nearly 3000km thick • Layer of hot rock • Temperature and pressure increase with depth • The uppermost part of the mantle and the bottom of the crust form the lithosphere • Soft layer in the mantle is the asthenosphere Material in it can flow slowly

5. Outer Core • Liquid • Nearly 2,300 km thick • Layer of molten metal that surrounds the inner core

6. Inner Core • Dense ball of solid metal • About 1,200 km thick • Such great pressure does not allow metals to spread out and become liquid

7. Earth’s Layers Recapitulation

8. What -o- sphere? • Lithosphere -the rigid layer made up of the uppermost part of the mantle and the crust • Asthenosphere- the soft layer of the mantle on which the lithosphere floats, although softer than the rest of the mantle, it’s still solid

9. Earth’s Magnetic Field • Scientist think movements of convection currents in the liquid outer core create Earth’s magnetic field

10. Convection • Heat transfer involving the movement of fluids – including liquids and gases • Caused by differences in temperature & density • A convection current is the flow that transfers heat within a fluid • The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion.

11. Convection in Earth’s Mantle • Convection Currents in the mantle occur as hot material from deep within the Earth rises while cooler material near the surface sinks. • Heat from the core and the mantle itself causes convection currents in the mantle. • Convection currents flow in the asthenosphere (upper mantle) • hot, less dense portions of the mantle rise and displace cooler, denser rocks, which then sink into the mantle

12. Cooler,  dense rocks sink in the mantle, whereas the warmer rocks within the mantle rise by a process called mantle convection (shown by red arrows in the diagram). • Convection plays an important role in the influencing the dynamic nature of the Earth.  Later we will discuss the importance of the sinking, cold portions of plates along the surface of the Earth (shown in tan). 

13. Convection and the Core • There are also convection currents in the outer core. These convection currents cause Earth’s magnetic field.

14. Earth’s Layers Review • The solid part of the Earth is the Lithosphere. It has 2 parts – the crust and part of the upper mantle. • The crust, or Lithosphere of the Earth is about 25 miles thick over the mountains, and about 4 miles thick under the ocean floor. • Below the lithosphere is the asthenosphere – where convection currents cause plate movements.

15. Continental Drift • It has taken the continents about 225 million years since the breakup of Pangaea to move to their present locations.

16. Moving Continents The belief that continents have not always been fixed in their present positions was first suggested as early as 1596 by the Dutch map maker Abraham Ortelius in his work Thesaurus Geographicus. Ortelius suggested that the Americas were "torn away from Europe and Africa . . . by earthquakes and floods"

17. Drifting Continents In 1858, geographer Antonio Snider-Pellegrini made these two maps showing his version of how the American and African continents may once have fit together, then later separated.

18. Drifting Continents However, it was not until 1912 that the idea of moving continents was seriously considered as a full-blown scientific theory -- called Continental Drift -- introduced by a 32-year-old German meteorologist named Alfred Wegener.

19. Alfred Wegener Alfred Lothar Wegener (1880-1930), the originator of the theory of continental drift http://pubs.usgs.gov/gip/dynamic/wegener.html

20. Evidence for Continental Drift Wegner based his theory on: • the puzzle fit of the coasts of the continents • the matching geologic features between continents now separated • the identical fossil plants and animals found on separate continents

21. Evidence for Continental Drift

22. Movement of Antarctica The discovery of fossils of tropical plants in Antarctica led to the conclusion that the frozen land previously must have been situated closer to the equator, in a more temperate climate where lush, swampy vegetation could grow.

23. www.mnh.si.edu/.../4_1_2_3_glossopteris.jpg The picture above is of Antarctica as it looks today – below is a picture of a tree as it would have looked and the fossils from this kind of tree – found in the frozen ground of Antarctica.

24. Past location of Antarctica http://maps.unomaha.edu/Maher/plate/week10/USGSDynamicEarthfossils.gif

25. Identifying Supporting Evidence • What evidence supports the hypothesis of continental drift? Evidence Shape of continents Hypothesis Earth’s continents have moved. Fossils Climate change

26. Plate Tectonics Plate tectonics is the theory that explains how the supercontinent, Pangea, broke up. In addition, plate tectonics helps us understand many changes in the Earth’s geology.

27. Plate Boundaries The regions where plates meet are called plate boundaries – these regions are active with different types of geological occurrences – depending on the type of boundary.

28. Types of Plate Boundaries • Three kinds of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries. A different type of plate movement occurs along each type of boundary.

29. Types of Plate Boundaries Type of Plate Boundary Type of Motion Effect on Crust Feature(s) Formed Crashing Plates move together. Convergent Oceanic-Continental Trenches & Volcanoes Subduction Crashing Plates move together. Convergent Continental-Continental Mountain building Mountains Pulling Plates move apart. Mid-ocean ridge, ocean floor, rift valley Divergent boundary Crust pulled apart by tension forces. Sideswiping Plates slide past each other. Transform boundary Strike-slip fault Crust is sheared.

30. Divergent Boundaries Where two plates spread apart, cracks or rifts form in the earth's crust. We see this force at work today in Iceland, where that island nation (and all of the middle of the Atlantic ocean) is spreading apart, and volcanoes are filling in the cracks with lava.

31. Plate separation is a slow process. For example, divergence along the Mid Atlantic ridge causes the Atlantic Ocean to widen at only about 2 centimeters per year.

32. Ocean Floor SpreadingMid-Atlantic Ridge The Atlantic ocean is spreading about 3/4ths of an inch per year. In your lifetime, North American will move westward the length of a man's body.

33. Subduction When two plates move toward each other, the denser one is forced under the other in a process called subduction.

34. Ring of Fire Deep trenches are formed when subduction happens in the ocean, also it gives rise to earthquake activity and volcanic islands. Japan is such a place, in the Pacific Ring of Fire.

35. Convergent Boundaries Places where plates crash or crunch together are called convergent boundaries. Plates only move a few centimeters each year, so collisions are very slow and last millions of years

36. Making Mountains On land, continents colliding cause the land to raise up, (geologists call it uplifting) and this force can build mountain ranges. Right now, India is colliding with the Eurasian Plate, causing the Himalayan Mountains. The Andes mountains of South America are the result of the partial melting of the plate being subducted, with the resultant molten rock (magma) rising through the continental crust and building a distinctive mountain chain down the length of that continent.

37. Transform Boundaries Places where plates slide past each other are called transform boundaries. Although transform boundaries are not marked by spectacular surface features, their sliding motion causes lots of earthquakes

38. Making Islands The Hawaiian Islands sit on the Pacific Plate. As this plate moves, it appears that it is moving over a "hot spot" in the mantle.

39. The Hawaiian island chain was formed from volcanic eruptions, but only one volcano is active at a time – the one over the hot spot.

40. The large island, Hawaii, is the most recent volcanic activity. Notice how the islands in the chain get progressively older –the result of the moving plate.