1. Continental Drift & Plate Tectonics

2. Continental Drift Theory
First proposed by Alfred Wegener in 1912:
250 million years ago, all of the continents were combined into one super-continent called “Pangaea”
The continents gradually drifted apart to where they are today
Wegner didn’t make up this theory out of the blue – like all scientists, he based it on evidence

3. Evidence Summary Geographic fit of South America and Africa
Fossils match across oceans
Rock types and structures match across oceans
Ancient glacial features

4. Geographic Fit
Continents look like they could be part of a giant jigsaw puzzle
Here’s how they moved apart

6. Fossils Match
Plant and animal fossils found on the coastlines of different continents

8. Fossil Fuel in Antarctica
Tropical plant remains (coal deposits) found in Antarctica
this is evidence that Antarctica was once much warmer and much closer to the equator, since tropical plants don’t grow in Antarctica today

9. Rock Structures Match Across Oceans
Same rock patterns found in South America, India, Africa, Antarctica and Australia

10. Rock Structures Match Across Oceans

11. Ancient Glacial Features
Glaciation in Africa, South America, India, and Australia during the same time

12. Ancient Glacial Features

13. Evidence but no Method
While Wegener presented compelling evidence, there was still no explanation for HOW the continents drifted.
The question remained: “If continents drift, what is making them move?”

14. Sea Floor Discoveries WW II: Military Spending
U.S. Navy mapped seafloor with sonar in order to help ships and submarines navigate.
They expected to find that the ocean floor was a vast, flat plain. What they found was shocking.

15. Sea Floor Discoveries
Instead of miles and miles of flat surface, they found that the ocean floor had:
oceanic ridges - submerged mountain ranges
fracture zones - cracks perpendicular to ridge
trenches - narrow, deep gashes
seamounts - drowned undersea islands

16. Sea Floor Discoveries
In addition, they discovered that the rocks of the seafloor included only basalt, gabbro, and serpentinite - no continental materials.
This suggested that the sea floor was not simply “covered up” continental crust, but was made of different materials and at a different time

17. Sea Floor Discoveries
Further study of these rocks led scientists to even more surprising information:
The sea floor’s youngest rocks were located right at the ocean ridge – and as you moved away from the ridge in either direction, the rocks got progressively older.

18. Sea Floor Discoveries

19. Sea Floor Discoveries
What scientists discovered was that the sea floor was being constantly “recycled.” The youngest rocks were created from magma rising to the surface, hardening and pushing aside the older rock.
Scientists called this process “sea floor spreading.”

20. Sea Floor Discoveries So now we know:
sea floor is being created at the mid-ocean ridges
sea floor is spreading
the oldest ocean floor occurs at the coastlines of continents…
Why doesn’t the earth get bigger? Where does the ocean floor go? Why doesn’t it get any older?

21. Sea Floor Discoveries
The ocean floor is pushed against the continental crust – and because it is denser, it dives under the crust.
This process is called subduction

22. The Rise of Plate Tectonics
In the late 1950’s, the United States was engaged in The Cold War with the Soviets
To keep an eye on Soviet nuclear tests, the U.S. military developed new, advanced seismometers
These seismometers were deployed in over 40 allied countries and were recording 24 hrs/day, 365 days/year

23. The Rise of Plate Tectonics
Besides nuclear tests, the seismometers recorded every moderate to large earthquake on the planet.
Scientists mapped the earthquake data and found something they weren’t expecting:
Armed with this high-precision earthquake data, seismologists found that activity happens in narrow bands.

24. The Rise of Plate Tectonics

25. The Rise of Plate Tectonics
The discovery of these bands led scientists to understand that the earth’s outer shell is broken into thin, curved plates that move laterally atop a weaker underlying layer.
Think of it like a hard-boiled egg: you can put cracks all over the shell of a hard-boiled egg, but the egg is still “whole”

26. Types of Plate Boundaries
The interaction of the plate edges with each other can be classified as one of three main types of boundaries:
Convergent boundaries
Divergent boundaries
Transform boundaries

27. Types of Plate Boundaries
Convergent: areas of plates that are moving toward each other
there are three sub-types of convergent boundaries:
oceanic to continental
continental to continental
oceanic to oceanic

28. Types of Plate Boundaries
Divergent: areas of plates that are moving away from each other

29. Types of Plate Boundaries
Transform: areas of plates that are sliding past each other

30. Types of Plate Boundaries
Here’s an animation of each type of plate boundary

31. Types of Plate Boundaries

32. Sea Floor Discoveries
Bill Nye discusses sea floor discoveries and plate tectonics

33. Review the Facts 1 pt 1 pt 1 pt 2 pt 2 pt 2 pt 3 pt 3 pt 3 pt Plate
Tectonics
Continental
Drift
Sea Floor
1 pt
1 pt
1 pt
2 pt
2 pt
2 pt
3 pt
3 pt
3 pt
Go To Exit Slip

34. Continental Drift 1 pt
The scientist who first proposed the theory of continental drift

35. Continental Drift 1 pt Answer
Who was Alfred Wegner?

36. Continental Drift 2 pt
fossils match across continents and oceans, same rock patterns found on five different continents, mountain ranges match across the Atlantic ocean

37. Continental Drift 2 pt Answer
What is some of the evidence Wegner used to support his theory that the continents were once joined?

38. Continental Drift 3 pt
Because he had no answer to the question, “If the continents are drifting, what mechanism is causing them to move?”

39. Continental Drift 3 pt Answer
Why was Wegner’s theory of continental drift widely ignored?

40. Sea Floor 1 pt
ocean ridges, fracture zones, trenches, seamounts

41. Sea Floor 1 pt Answer
What did Harry Hess and the US Navy discover when they mapped the sea floor using sonar?

42. Sea Floor 2 pt
The process of ocean crust “diving” under other crust into the mantle

43. Sea Floor 2 pt Answer
What is subduction?

44. Sea Floor 3 pt
The process by which the newest ocean floor is created at mid-ocean ridges, pushing older crust outward

45. Sea Floor 3 pt Answer
What is sea floor spreading?

46. Plate Tectonics 1 pt
What the earth’s outer shell is broken into

47. Plate Tectonics 1 pt Answer
What are plates?

48. Plate Tectonics 2 pt
Instrument deployed by US Military to spy on soviet nuclear tests which also detected medium-to-large earthquakes.

49. Plate Tectonics 2 pt Answer
What is a seismometer?

50. Plate Tectonics 3 pt
The three ways plate boundaries interact

51. Plate Tectonics 3 pt Answer
What are convergent, divergent, & transform?

52. Review – Exit Slip
Choose what you believe to be the strongest piece of evidence Wegner uncovered to support the idea of continental drift and explain why you think it is the most convincing.
If new sea floor is constantly being created, why isn’t the earth growing in size?
How did earthquakes help scientists to understand the structure of the earth’s crust?

53. THE FINE PRINT
© Jan Parker, 2010 – for purchaser’s classroom use only; please do not distribute. If other teachers in your school like what they see, send them to my website or to my web store 
If you put your classroom materials on a server for your students, please post this presentation in pdf form. Thanks!

54. Continental Drift and the Changing Oceans
Panthalassa

55. Important Events – 225 mya
Pangaea was surrounded by single ocean called Panthalassa which would become the modern Pacific Ocean.
Thethys Sea, the precursor of the Mediterranean Sea, separated Eurasia from Africa.
The Sinus Borealis would become the Arctic Ocean.

56. Important Events – 200 mya
Rift appears between North America and combined South America and Africa.
Was the beginning of the Mid-Atlantic Ridge and created the North Atlantic Ocean
Pangaea was separated into 2 large continents – Laurasia (North American and Eurasia) and Godwana (South America, Africa, India, Antarctica, and Australia).
At the same time, a rift began to separate India from Godwana creating the Indian Ocean

57. Important Events – 135 mya
South Atlantic Ocean was born as a rift separated South America from Africa.
This rift joined the mid-ocean ridge in the North Atlantic to form a single Mid-Atlantic Ridge.
The growth of the Atlantic Ocean caused the Americas to drift further from Africa and Eurasia.
To make room for the new seafloor created in the Atlantic, the Pacific Ocean shrank.

58. Important Events – 65 mya
The Y-shaped rift that created the Indian Ocean continued to grow and worked to separate Australia from Antarctica.
The base of the rift formed the Red Sea.
India moved North until it crashed into Asia creating the Himalayas.

59. Records in the Sediments
Scientists can tell a lot about the Earth’s history by examining the types of sediments laid on the ocean floor.

60. Marine Sediments Lithogenous Sediment Biogeneous Sediment
Derived from weathering of continental rocks
Large particles sink while finer material is carried away in ocean currents.
Coarse lithogenous sediments are deposited near continental edge.
Consists of the skeletons and shells of microscopic marine organisms – radiolarians, diatoms, foraminiferans
AKA microfossils
Can tell scientists what organisms lived in the ocean in the past and can indicate ancient ocean temperatures
Carbon dating can determine age of microfossils

61. Biogenous Sediment

62. Sea Level Changes

64. Structure of the Sea Floor
Because the ocean floor is created/destroyed due to the workings of plate tectonics, major features are similar from place to place worldwide

65. Sea Floor Continental Margins Deep Sea Floor
Submerged edges of continents
Boundaries between continental crust and oceanic crust
Consist of continental shelf, continental slope and continental rise
Most lies at a depth of m
Aka abyssal plains
Dotted with abyssal hills seamounts, guyots
Trenches and ridges
Hydrothermal vents

66. Continental Margin

67. Continental Shelf Shallowest part of the continental margin
Biologically richest with most life and best fishing
Composed of continental crust that is submerged
Were exposed during past times of low sea level

68. Continental Shelf and Politics
The continental shelf is an underwater extension of land that can stretch out to sea for many kilometres. Government scientists are studying the Canadian continental shelf in the Atlantic Ocean as part of the Extended Continental Shelf (ECS) Program, a large initiative set up to identify characteristics of the shelf under the Atlantic and Arctic Oceans. The aim of the Program is to define the outer limits of the shelf where it extends beyond 200 nautical miles (NM) from coastal baselines, thereby determining with precision where Canada may exercise its existing sovereign rights over the natural resources of the seabed and subsoil. The scientific data collected as part of this initiative will be used for Canada’s submission to the United Nations Commission on the Limits of the Continental Shelf (CLCS).

69. Continental Slope
Begins at the shelf break and descends down to the sea floor
Water becomes colder and more sluggish.
Oxygen levels decline; pressure increases
Ocean life along the continental slope must be much more tolerant of extreme conditions.

70. Continental Rise
Formed by sediments accumulating on the sea floor at the base of the continental slope
The continental rise is often used as an indicator by ships, since it indicates that the continental shelf, and land, are close by.

71. Nature of Continental Margins
Active Margin
Passive Margin
Exists at plate boundaries notably subduction zones
Characterized by steep, rocky shorelines and intese geological activity (earthquakes, volcanoes)
Narrow continental shelf and steep continental slope lead to a trench or a poorly developed continental rise
Exists in geologically inactive zone
Characterized by flat coastal plains
Wide continental shelf and gradual continental slopes, and thick continental rises

72. Continental Margins

73. Abyssal Plains
Underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 metres.
Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth’s surface.
They are among the flattest, smoothest and least explored regions on Earth.
Seamounts and hydrothermal vents are found here
Home to a tremendous variety of marine life

74. Biodiversity in the Deep Ocean

76. Seamounts Seamounts are volcanic mountains arising from the sea floor.
Some are flat-topped and are called guyots

77. Bowie Seamount
Bowie Seamount is the shallowest submarine volcano in Canada
Rises 3000 m from the ocean floor to within 24 m of the water’s surface
Because of its biological richness, Bowie Seamount was designated as Canada's seventh Marine Protected Area on April 19, 2008 under the Oceans Act
To the Haida Nation, the submarine volcano is called Sgaan Kinghlas. In their language it means "Supernatural Being Looking Outward“
Recognized as a hazard to navigation and is avoided by shipping vessels.

78. Hydrothermal Vents
Commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots
May form features called black smokers
Biologically productive
Chemosynthetic bacteria form the base of the food chain