Section 17.1 and 17.2

1. Section 17.1 and 17.2 Plate Tectonics, Earthquakes, and Volcanoes

2. Background – History of the Earth This chapter is based on the idea that Earth is about 4.5 billion years ago. • Began as a ball of small particles pulled together by gravity. As pressure built, the material heated up.

3. Possible explanations for the heat: - collisions of particles - compression of the interior of the planet - radioactive decay of some natural elements • The Earth began to cool and the heavier (more dense) elements sank while the lighter (less dense) materials floated to the surface.

4. 17.1 Earth’s Interior and Plate Tectonics The Earth’s Interior is divided into 4 basic layers

5. Crust - Outermost and thinnest layer of Earth = 4 - 40 km thick - Made of hard, solid rock - Can be either continental crust (thicker) or oceanic crust (thinner) - The crust (and part of the mantle) is divided into 7 large plates

7. Mantle - Thickest layer of Earth = 2900 km thick - 80 % of Earth’s volume - Scientists have never drilled to the mantle, so they can only guess what it is made of based on what we learn from earthquakes and volcanoes. - outer mantle is made mostly of solid rock - inner mantle is made of hot and melting rock - rich in iron, magnesium, silicon, and oxygen

9. Outer Core - surrounds the inner core with liquid metal boiling under pressure: nickel and iron • Inner Core - made of solid metal: nickel and iron Temperatures increase as one gets closer to the center of the earth.

11. Plate Tectonics = the theory that the Earth’s surface is made up of large moving plates. • Alfred Wegner studied world maps and hypothesized about Pangea – a supercontinent that he believed existed in history and split into the current continents.

13. Continental drift = the mechanism for the movement of continents caused by interactions between: • Lithosphere - the earth’s stiff outer shell made of the crust and hard upper mantle - divided into 7 large pieces and several smaller pieces called tectonic plates.

15. Asthenosphere - the liquid inner mantle which is in constant slow movement because of the heating from the center of the earth - convection currents result from the liquid rock being heated near the core and rising toward the outer mantle then cooling

16. Interaction = currents in asthenosphere push the lithosphere plates like waves push around floats

17. Evidence supporting continental drift • The shapes match Ex: South America fits with Africa like puzzle pieces • The plants and animals match Ex: identical fossils along the coastal parts of Africa and South America • The rocks match Ex: the same type of broad belts of rocks in Africa and South America; these bands have alternating magnetic polarities

18. Shapes match

19. Plants and Animals Match

20. The ice marks match Ex: Glacial striations on rocks show that glaciers moved from Africa onto South America without drifting away in the Atlantic Ocean • The current positions don’t match Ex: coal that is mined in Pennsylvania was actually formed from tropical plant life that lives near the equator.

21. Basic Types of Plate movement Plate movement occurs at faults, which are any cracks in the earth where movement occurs. There is are forces at each fault (convection currents) that cause movement in a certain direction. We use the direction to categorize the fault into a boundary. Plates move about 2 cm to 10 cm a year.

22. Three types of boundaries: divergent, convergent, transform. • Three types of faults: normal, reverse, strike slip • Three types of forces: tension, compression, shear

24. Divergent Boundaries • Two plates are moving apart leaving gaps; the gaps are filled with magma rising from the mantle which cools into new crust

25. Occur at normal faults • Caused by tension force

26. Movement results in volcanoes and oceanic rift valleys surrounded by high mountains. - Mid-Atlantic Ridge = a submerged mountain range under the Atlantic Ocean

27. Mid-Atlantic Ridge

28. Iceland on a Divergent Boundary

29. Convergent Boundaries • Two plates are moving towards each other

30. Occur at reverse faults • Caused by compression forces

31. Movement results in subduction zones which create ocean trenches, mountains, and volcanoes. - subduction = when one plate dives beneath another; the lower plate is often melted by the heat of the asthenosphere • - Andes Mountains in South America where a continental plate and an oceanic plate meet - Mariana Trench in Pacific Ocean near Japan where two oceanic plates meet is more than 11km deep (6.8 mi) - Himalayan mountains are due to the collision of two continental plates

32. Transform Boundaries • Two plates are moving horizontally past each other like two cars on a road going in opposite directions

33. Occur at strike slip faults • Caused by shear forces

34. Movement results in earthquakes - San Andreas fault runs from Mexico through California

36. 17.2 Earthquakes and Volcanoes What are Earthquakes? • Vibrations from rocks sliding past one another • Occur mostly at plate boundaries; all three types of the boundaries.

37. What happens? • As plates move, pressure builds and the rock eventually breaks at the focus. This releases seismic waves in all directions around the focus.

38. There are three types of energy waves: - longitudinal waves (primary waves or P waves) move like a compressing spring or a slinky. They are the fastest and first waves that run through rock

39. - transverse waves (secondary waves or S waves) move like a shaking rope and are slower than P waves

40. - surface waves only move across the Earth’s surface in a rolling motion; cause more destruction

41. The epicenter is the point on the earth’s surface directly above the focus.

42. Seismology – the study of earthquakes • Seismographs are machines that record info about the three types of waves sent out by an earthquake. • Measure ground motion in three directions (North to South, East to West, up and down) using inertia. • 1000 seismograph stations across the world; three are needed to triangulate an earthquake’s movement.

43. Richter Scale • a measure of the energy released at the focus of an earthquake • the magnitude is recorded from 2.0 to 10

45. Volcanoes • Any opening, or vent, through which magma reaches the Earth’s surface.

46. Magma = molten rock under the surface of the earth • Lava = magma has reached the surface • Tephra = materials of all types that erupt from a vent; ash, cinder The makeup of the magma and type of eruption determines the type of volcano

47. Shield Volcanoes • Magma is rich in iron and magnesium which flows easily and far • Several mild eruptions • Creates many layers of lava into a gently sloping mountain • Ex: Mauna Lao in Hawaii

49. Composite Volcanoes • Magma is rich in silica; thicker; filled with gas bubbles • Gases cause alternating lava flows then an explosion of cinders and ash • Creates alternating layers of ash, cinders, and lava • Ex: Mount St. Helens • Seamount volcanoes are found underwater and resemble composites