Marine Science: Chapter 3 Part One Plate Tectonics

1. Marine Science: Chapter 3 Part One Plate Tectonics

5. 3.1 Earth’s Interior • The most detailed information we have about the interior comes from studying seismic waves. • 2 types of seismic waves: surface waves (slower, travel along the Earth’s surface) and bodywaves (faster, travel through Earth’s interior)

7. 2 Kinds of Body Waves • 1. P-wave: primary wave, travels fastest, arrives first at recording station • 2. S-wave: secondary wave, slower, second wave to arrive at recording station

11. P-waves • Known as compressional waves or push – pull waves • Can travel through all 3 states of matter: solid, liquid, and gas

14. S-waves • Also known as shear waves • Travel at right angles to the direction of motion • Travels only through SOLIDS

18. Internal Layers • Inner core: Solid, made up of iron and nickel and is 5 times as dense as common surface rocks because of the tremendous pressure at that depth • Outer core: Liquid, made up of iron and nickel, S-waves do NOT pass through the outer core

20. Internal layers Cont. • Mantle: makes up about 70% of Earth’s volume, solid and mobile, made up of magnesium – iron silicates • Crust: outermost layer, cool, rigid, thin • Moho: chemical boundary between the crust and mantle, rocks on either side have a different chemical composition, discovered by AndrijaMohorovicic

22. 2 Kinds of Crust Continental crust: low in density, avg. 25 miles thick, primarily granite Oceanic crust: more dense, avg. 4.3 miles thick, primarily basalt

23. oOc Oceanic

25. Isostasy • Is a balance kept in the mantle between land masses and oceanic crust • If material is removed from or added to the continents, isostatic adjustment occurs

27. Movement of the Continents • Alfred Wegener, came up with a theory called continental drift. He proposed the idea of a single supercontinent called Pangaea.

29. Wegener’s based his idea on: • Geographic fit of continents

30. Wegener Cont. • Rock type and structures matched

31. Wegener Cont. • Fossils more than 150 million years old collected on different continents which were similar, implying the ability of land organisms to move freely from one landmass to another.

32. Wegener cont.

33. Final Wegener • The weakness in Wegener’s theory was the inability to identify a mechanism that could cause the continents to break apart and drift through the ocean. Little attention was given to his theory after his death.

34. H. H. Hess: Convection Cells • Early 1960’s, Hess came up w/ the concept that deep within the Earth’s mantle are currents of low-density molten material that is heated by Earth’s natural radioactivity that moves upward. At the base of the lithosphere it moves horizontally beneath the lithosphere, starting to cool and becomes more dense and sinks downward again. • This pattern of moving mantle material is called convection cells

35. A Convection Cell Model

36. Seafloor Spreading • At the mid-ocean ridge, upward-moving mantle rock would carry heat w/it toward the surface. • The heat would cause the ocean crust to expand, or move and this created the mid-ocean ridge. • Volcanism along the ridge results in magma getting out onto the sea floor, where it cools and hardens, and creates new sea floor and oceanic crust, pushing older sea floor away from the ridge. • This lateral movement of the oceanic lithosphere produced seafloor spreading.

37. Convection/Seafloor Spreading Model

38. Seafloor Spreading Cont. • The continents are being carried on the lithosphere away from the mid-ocean ridge. • The older crust will be destroyed at deep-sea trenches, a subduction zone. • Mantle convection currents and seafloor spreading, proposed by Hess, work together to incorporate the idea of Plate Tectonics.

39. Glomar Challenger • The cores taken by the Challenger provided much of the data needed to establish the existence of seafloor spreading.

41. Dipole: 2 opposite poles

42. Magnetic Field Information • Caused by a steel ball (inner core) spinning inside the liquid outer core, makes our magnetic field, which gives us a north and south pole. This flips around and the reason why is not known. Visualize a top spinning that starts to wobble and falls over. • Evidence of magnetic field reversals (polar reversal) are seen in the study of paleomagnetism. Volcanic rocks as they cool “freeze” magnetic orientation because of the iron in igneous rock.

43. Evidence for Crustal Motion

45. End of part 1, Chapter 3