Download Geology Chapter 14

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Geology Chapter 14 – The Ocean Floor
Michael Wysession Washington University
Big Ideas Seventy-one percent of Earth's surface is covered by ocean water. There are four main ocean basins: the Pacific,
Atlantic, Indian, and Arctic. The bathymetry of the ocean seafloor is very varied, a result of many different geological
processes.
Space and Time The margins of continents (including the continental shelf, slope, and rise) are often under sea water.
The ocean floor is deepest at trenches, where oceanic lithosphere sinks back into the mantle. The seafloor bathymetry also
varies with the presence of seamounts, fracture zones, and mid-ocean ridges. Ocean sediments (formed chemically,
biologically, or carried in from the continents) cover most of the ocean floor. These sediments are shallowest at mid-ocean
ridges, and often thickest along continental margins.
Forces and Motion The ocean seafloor forms at mid-ocean ridges, which rest higher than the surrounding basin seafloor
because the new rock is hot and buoyant. Hot water circulating through the mid-ocean ridge system removes metals and
minerals from the crust out of hydrothermal vents.
Matter and Energy A variety of technologies are used to investigate the ocean. Sonar is used to map seafloor
bathymetry. Microwaves transmitted from satellites are used to map the ocean surface and seafloor features. Underwater
submersibles directly investigate the seafloor.
Earth as a System The ocean is the source of many important natural resources such as oil, natural gas, gas hydrates (as
of yet untapped), sand, gravel, salts, and metals.
Section 1 – The Vast World Ocean
1. What are two nick names for the Earth?
2. How much of the Earth is covered by oceans?
3. What is oceanography?
4. If the area of the Earth is 510 million square kilometers, how much of it is represented by oceans and smaller
seas?
5. What are the four main ocean basins?
6. Which is the largest? How large?
7. Which is the deepest? How deep?
8. List the oceans in order from the largest to smallest and give their relative depths.
9. How is the topography of the ocean floor similar to that of the continents?
10. Define bathymetry.
11. When did the first understanding of the ocean floor’s varied topography unfold?
12. What does today’s technology allow scientists to do?
13. What is sonar?
14. Briefly describe how sonar works.
15. How do satellites help us learn about the shape of the seafloor?
16. What is a submersible?
17. When was the first submersible used and by whom?
Section 2 – Ocean Floor Features
18. Name the three ocean floor regions.
19. What is known as the continental margin?
20. In the __________________ Ocean, __________________ layers of undisturbed __________________ cover the
continental margin. This region has very little __________________ or __________________ activity.
21. Describe the continental shelf.
22. What do continental shelves contain?
23. Describe the continental slope.
24. What are submarine canyons?
25. What are turbidity currents?
26. Turbidity __________________ are known to be an important mechanism of __________________ transport in
the ocean. Turbidity currents __________________ submarine canyons and __________________ sediments on
the deep-ocean floor.
27. Describe the continental rise.
28. Where is the ocean basin floor and what does this region include?
29. What are deep-ocean trenches?
30. Where do trenches form?
31. How did the margins of the Pacific Ocean get the nickname Ring of Fire?
32. Describe abyssal plains.
33. The sediments that make up the abyssal plains are carried there by __________________ currents or
__________________ as a result of __________________ sediments settling.
34. Which ocean has the most extensive abyssal plain and why?
35. What are seamounts?
36. What happens when a seamount reaches the ocean surface?
37. What is the mid-ocean ridge and where is it found?
38. Where does seafloor spreading occur?
39. How is new ocean floor formed at mid-ocean ridges?
40. Describe hydrothermal vents.
Section 3 – Seafloor Sediments
41. How can ocean-floor sediments be classified?
42. Name the three broad categories ocean-floor sediments categories.
43. Describe terrigenous sediment.
44. Describe biogenous sediment.
45. What is the most common biogenous sediment and what is it composed of?
46. Name the other two biogenous sediment.
47. What is siliceous ooze made of?
48. What does hydrogenous sediment consist of?
49. Name three of the most common types of hydrogenous sediments.
Section 4 – Resources from the Seafloor
50. The __________________ floor is rich in __________________ and __________________ resources.
Recovering them, however, involves __________________ challenges and high __________________.
51. What are the two main energy products currently being obtained from the ocean floor?
52. What is the source of today’s deposits of oil and natural gas?
53. What is one environmental concern about offshore petroleum exploration?
54. What are gas hydrates?
55. What is the most common type of natural gas?
56. Where do gas hydrates occur?
57. When are most oceanic gas hydrates created?
58. An estimated __________________ cubic meters of methane are locked up in __________________ containing
gas hydrates.
59. What is one drawback to using gas hydrates as an energy source?
60. Name and briefly describe three other major resourced from the ocean floor.