Earth's Interior Layers and Plate Tectonics

1. Chapter 12 Section 3: Earth’s Interior Section 1: Evolution of Earth’s Crust Section 2: Earthquakes Section 4: Volcanoes

2. Section 3: Earth’s Interior

3. Basic Layers of the Earth • From the surface to the center: • Crust • Mantle • Outer Core • Inner Core

4. Earth’s Crust • The crust is the thinnest layer. • The crust is a rocky layer. • There are two types of crust: 1.) oceanic 2.) continental

5. Two Types of Crust • Oceanic Crust- the rock beneath oceans • Oceanic crust is made mostly of a rock called basalt. • Easy way to remember this is ba“salt”- salty like the ocean… • Basalt is a very dense (heavy) rock. • Continental Crust- the rock of continents • This crust is made mostly of a rock called granite. • Granite is less dense than basalt.

6. Where the 2 Types of Crust Meet: • If oceanic crust moves and runs into continental crust, the oceanic crust will sink beneath. • This is because basalt is more dense than granite. • This is called subduction.

7. subduction Magma

8. The Mantle • The mantle is the thickest layer. (2,900 km) • The mantle is divided into layers: • upper mantle and crust = rocky lithosphere • Middle mantle = gooey asthenosphere • Lower mantle = magma ROCK MAGMA

9. The Lithosphere • “Lithos” means rock. • The crust and the upper mantle are both hard, rocky layers. • Together they are called the lithosphere. • The whole Earth is covered in lithospheric rock, but 70% of it is hidden by oceans. • The lithosphere is broken into pieces called “plates” or “lithospheric plates.”

10. About the Plates: • There are more than a dozen (12) plates. • The U.S. is mostly on the North American plate with the exception of Baja California and Hawaii which are on the Pacific Plate.

11. The Asthenosphere • The asthenosphere is the part of the mantle that flows gently like melted plastic or gooey caramel. • Currents of magma in the mantle make the plates, which are floating on top of the mantle, move around.

12. Convection Currents • Magma in the upper mantle is a cooler 1,600°F. • The magma in the lower mantle is around 4,000°F. • The hot magma rises and the cooler magma sinks. • This creates a convection current.

13. Moving Plates • The rocky lithospheric plates float along on the convecting magma of the asthenosphere. • This causes plates to run into each other creating earthquakes and mountains. • Convection currents can also make the plates move away from each other creating valleys.

14. The Outer Core • Under the mantle lies the outer core. • The outer core is composed of the metals of nickel and iron. • The outer core is so hot that it melts the iron and nickel into liquids. • Temperatures near the top of the outer core are around 4,000°F, but at the bottom the temperature is a much hotter 9,000°F!

15. The Inner Core • The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together to create a solid ball of metal. • This extremely hot, dense, ball of metal is able to spin in place because it is surrounded by the liquid outer core.

16. Why the Layers? • Scientists believe that as Earth’s materials cooled, the densest materials collected at the center of the Earth and the less dense materials at the surface. • This change in density is called a discontinuity.

17. How Do We Know? • Earthquakes produce seismic waves that move through the Earth. • There are P and S waves. • P waves can travel through liquids and solids. • S waves cannot travel through a liquid. • Scientists studied the way these waves move through the Earth and were able to draw conclusions leading to what we know today about the layers of the Earth.

18. Section 1: Evolution of Earth’s Crust

19. Continental Drift & Pangaea • In 1915 Alfred Wegener suggested that Earth’s continents were once part of a large super-continent called Pangaea. • Pangaea was thought to have broken into pieces 200 million years ago and drifted apart. • Wegener was never able to explain what caused the continents to move. • After his death, in 1930, evidence was found.

20. Why Did He Believe This? • Wegener used three pieces of evidence to support his theory: 1.) Matching coastlines: The east coast of South America looks like it fits with the west coast of Africa. 2.) Matching fossils: The same fossils from ferns and dinosaurs are found on multiple continents. 3.) Matching rocks and mountain ranges: Mountain ranges on the coasts of different continents have matching rock types.

21. Matching Coastlines:The light blue continental shelf is the continental crust under water that has not been as affected by weathering as the land above water. It’s a nearly perfect match for coastlines.

22. Matching Fossils

23. Matching Mountain Ranges

24. Sea Floor Spreading • After WWII Dr. Harry Hess made an accidental discovery while using sonar intended to detect submarines. • The sonar created a map which showed a crack in the ocean floor where magma was coming out and forming a mountain on both sides of a valley.

25. MOR (Mid Ocean Ridge) • Hot magma from the mantle moves up toward the crust because of its low density. (Hot things expand and become less dense) • If there is a weak area in the crust it will crack and create a fault. • The magma will come out of the crack, upon which it becomes lava. (MAgma is in the MAntle, Lava has Left) • The crack in the ocean is called the “Rift Valley.” • The lava builds up on both sides of the valley, layer upon layer and creates a mountain on each side called the Mid Ocean Ridge. Rift Valley Hot magma rises up through a weak spot in the crust.

26. Mid-Ocean Ridge Around the Globe

27. Which crust is older? New Oceanic Crust is Forming Oldest Rock Oldest Rock Older Rock Older Rock Newest/ Young Rock Mantle Mantle

28. Theory of Plate Tectonics • Plate tectonics- The theory that pieces of the Earth’s lithosphere are in constant motion, driven by convection currents in the asthenosphere layer of the mantle. • J. Tuzo Wilson is credited with developing and explaining this theory.

29. Plate Boundaries • Since the lithospheric plates covering Earth’s surface are in constant motion, it causes them to bump, grind, slide, subduct, or pull apart from each other…. • There are three main types of plate boundaries: 1.) Divergent 2.) Convergent 3.) Transform

30. Divergent Plate Boundary • Divergent Boundary- where two plates move away from each other (divide). • This usually creates a valley.

31. Convergent Plate Boundaries • Convergent Boundary occurs when two plates collide (come together). • There are three ways these form: 1) Oceanic crust collides with continental crust 2) Oceanic crust collides with oceanic crust 3) Continental crust collides with continental crust

32. Convergent #1: Oceanic and Continental Crust • The more dense oceanic crust subducts beneath the continental crust. • This causes the oceanic crust to melt and become part of the asthenosphere. • You would find a deep trench in the ocean where the plate subducts.

33. Convergent #2: Oceanic and Oceanic Crust • Two slabs of oceanic crust converge and create deep sea trench and a volcanic island arc • Examples: Japan, Alaskan Aleutian Islands, Ring of Fire

34. Convergent #3: Continental and Continental • Two slabs of continental crust converge and create folded mountains and plateaus. • Examples: Himalayas in Asia, Ural Mountain Range

35. Transform Plate Boundary • Transform Boundary- where two plates slide past each other. • This usually causes earthquakes. • Example: San Andreas Fault in California.

36. Section 2: Earthquakes

37. What’s an Earthquake? • Any seismic vibration of Earth caused by the rapid release of energy is an earthquake.

38. Earthquake Location and Depth • Most earthquakes occur at plate boundaries. • It is the grinding of the lithospheric plates trying to move past each other that causes the Earth to quake. • Divergent boundaries cause shallow earthquakes. • Convergent boundaries cause deep earthquakes because of subduction.

39. Focus vs. Epicenter • The point inside the Earth where the earthquake begins is called the focus. • Energy moves out away from the focus in rings that travel in all directions. • The waves eventually reach the surface. • The point on the surface that is directly above the focus is called the epicenter.

40. Earthquake Locations

41. Natural and Man Made: • In nature, stress can build up in the lithospheric rock until the rock moves and causes an earthquake. • Humans can cause the Earth to shake also. • Ex: trains, dynamite, low-flying planes…

42. Deformation • Deformation is the process of rocks changing shape. • This can be caused by 4 types of stress: 1.) Compression 2.) Tension 3.) Shearing 4.) Torsion

43. Types of Stress

44. Com“press”ion • Stress caused when rocks (Earth’s plates) move towards each other and squeeze. • This stress happens at convergent plate boundaries.

45. Tension • Stress caused when rocks move away from each other and become thinner. • Easy way to remember: When you get pulled in many different directions (school, friends, family, homework…) you may get a tension headache. • This stress happens at divergent plate boundaries. adf

46. Shearing • Stress caused when rocks move past each other and rub. • Easy way to remember: the blades of scissors “shears” rub past each other. • This stress happens at transform plate boundaries.

47. Torsion • This stress happens when rocks twist. • This happens when stresses act on rock from several different directions.

48. Elastic Deformation • In this type of deformation: • Stress acts on rock • The rock changes shape • The stress stops or is removed • The rock “rebounds” or “Springs” back into its original shape. • Hint: This is like an elastic rubber band. • This elastic rebound causes a sudden release of energy that causes earthquakes.

49. Plastic Deformation • In this type of deformation: • Stress acts on rock • Rock changes shape • The stress is removed or stops • The rock remains bent. There is no elastic rebound. Therefore, there is no earthquake.

50. Fault vs. Fracture • A fault is a crack in the Earth’s crust where motion occurs causing an earthquake. • Ex: San Andreas Fault in California • A fracture is a crack in the Earth’s crust that has no motion, therefore, no earthquakes.