1. Geography of the Oceans

2. Geography of the Oceans
Oceans cover
~ % of Earth’s surface
Divided into 4 basins
Pacific
Atlantic
Indian
Arctic
Shallow Seas
Mediterranean, Gulf of Mexico and S. China Sea connect main oceans
Basins connect at
Exchange of seawater, materials, & some migration paths 71
South Pole

3. Geology Basics

4. Structure of the Earth Thought to have formed 4.6 B years ago
Dust & particles left from the Big Bang
As Earth cooled
Particles settled by
Divided into 4 layers
density

5. Inner Core Mostly composed of iron alloys Solid Thickness 1221 km
Temp.
~ 6000 °C (10,832 °F)

6. Outer Core Composed of iron and nickel Liquid Thickness 2259 km Temp.
Produces Earth’s magnetic field
Thickness 2259 km
Temp.
~ °C ( °F)

7. Mantle “Plastic” Boundaries Thickness 2891 km
Hot temps make it flow like a liquid
Crust “floats” on top
Causes plate movement
Boundaries
Moho Discontinuity (Crust boundary)
Gutenberg Discontinuity (Core boundary)
Thickness 2891 km
Upper
Lower

8. Crust Outermost layer of Earth Extremely thin 46.6% oxygen! 2 types
ranges 7-70 km
46.6%
oxygen!

9. Cont. vs. Oceanic Crusts Cont. Oceanic Granite Basalt
Density = 2.7 g/cm3
Thickness is 7-70 km
Oldest rocks
> 3.8 billion years old
Oceanic
Basalt
Density = 3.0 g/cm3
Thickness 10 km or less
Oldest rocks
< 200 million years old

10. Plate Tectonics – “To Build”

11. Earth’s Lithospheric Crust
Divided into “plates”
Major & Minor
Makes up
Crust and upper mantle
Covers up
Lower mantle, outer core and inner core
Plates move in different directions
Cracking of the crust

12. Plate Boundaries

13. Plate Boundaries & Seismic Activity
Plate boundaries can be identified
Studying seismic activity

14. Major Lithospheric Plates
North American
South American
Pacific
Eurasian
African
Nazca
Indo-Australian
Antarctic

15. Types of Plate Boundaries
CONVERGENT BOUNDARY

16. Ocean vs. Ocean Boundary
Di = “two”
Divergent
Moving apart
Composed of basalt, iron, and silicon
High density rocks
Mid-Ocean Ridge and seafloor spreading

17. Cont. vs. Cont. Boundary Con = “with” Convergent collision
Move together
Granite, silicon, and aluminum
Lower density rocks
Mountain building
Ex: Himalayas, Atlas Mountains
Con = “with”

18. Ocean vs. Cont. Boundary Subduction zone
Plate edges override or slide past others
Less dense cont. plate overrides the denser oceanic plate
Oceanic plates subduct down into the mantle & are remelted
Results in trenches and volcanoes
Ex. Peru/Chile Trench

19. Peru/Chile Trench

20. Pangaea/Seafloor Spreading

21. Background Proposed by Alfred Wegener Why? Widely unaccepted 1912
Thought all continents were one huge land mass that later broke apart
Why?
Continent’s shapes roughly fit together like a puzzle
The rocks and fossils on different continents matched
Widely unaccepted
Convection cells - magma
He was a meteorologist, not a geologist

22. Break-up of Pangaea

23. Background (cont.) H. Hess and J. Wilson
1960’s Proposed mechanism for continental drift
Named “Geo-poetry” to avoid criticism

24. Background (cont.) Glomar Challenger
Drilled series of holes in Mid-Atlantic Ridge (Deep Sea Drilling Project)
Findings
Continental rocks date the Earth to about 4.5 billion years old
Law of Superposition
Oldest rocks at bottom & younger rocks above
Found no rock older than 3 billion years old with many being much younger

25. Background (cont.) Core samples from Mid-Ocean Ridges (MOR)
Matching magnetic striping in rocks on both sides
Project FAMOUS
1977
Alvin photographed magma squeezing out of MOR
Creation of new sea floor

26. New Theory – Sea Floor Spreading
Vine and Matthews
Scientists/Geologists used all data for new theory on plate tectonics
Theory of Sea Floor Spreading
Explained continental drift
Wegener was correct

27. Ocean Floor Bathymetry (Intro)
Depth
Metry =
Measure
Ocean Floor Bathymetry (Intro)
Oceanic bathymetry is similar to continental topography except continent features are smaller due to erosion
M.O.R.

28. S.O.N.A.R.
Structures on ocean floor mapped by SOund Navigation And Ranging
Echo sounding
Equation
Depth = time * 1484 m/s
2 (round trip)
[1484 m/s = speed of sound in water]

29. Division of the Ocean Floor
Basins – deep ocean
Abyssal plain
Abyssal hill
Seamount
Island
Guyot
Trenches
Mid-Ocean Ridge (MOR)
Rift valley
Margins – shallow
Continental shelf
Continental slope
Submarine Canyons
Turbidity currents
Continental rise

30. Transition from continent to deep ocean basins
Bathymetry Margins
Transition from continent to deep ocean basins

31. Continental Shelf Underwater extension of the continent
Most biologically productive area
Why?
High light availability

32. Continental Slope Very steep cliff into basin
Usually 1-2 mile drop-off
Materials tumble down slope
Form turbidity currents
Cut canyons into slope

33. Turbidity currents on slope

34. Continental Rise Sediment “speed bump”
Accumulation of sediment at base of continental slope
Found b/w cont. slope & abyssal plain

35. Parts of the Basins

36. Abyssal Plain Flat, featureless region Common Rare Similar to a desert
Atlantic and Indian Oceans
Rare
Pacific Ocean

37. Abyssal Hill Domes of sediment deposition that shift
Similar to sand dunes on land
10 – 300m small

38. Seamount Underwater volcanoes Summits do not break the surface!
Must raise at least 1000m off of seafloor
Forced up by
magma

39. Island Seamounts extending up & out of the water
Yellow (hot spots)
Seamounts extending up & out of the water
Differ from continents because they have no margins
Usually associated with “hot spots”
Active volcanoes
Ex: Hawaiian Islands

40. Guyot Islands shortened by weathering and erosion Start out as islands
Reclassified as W & E occur and re-submerge feature
Similar to land plateaus

41. Trench Subduction zones Form boundary around Pacific plate
Basalt is re-melted into asthenosphere
Top portion of mantle
Form boundary around Pacific plate
Ring of Fire
Seismic & volcanic activity

42. Mid-Ocean Ridge (MOR)

43. Mid-Ocean Ridge (MOR) Longest mtn. range in the world
40,000 miles long
Covers % of Earth’s surface
Divergent plate boundary
New seafloor is being formed
Iceland
Large section of MOR extending above the water
Due to sitting on a “hot spot” 23

44. Rift Valley Vent resulting from divergent plate boundaries
Allow magma to recreate new ocean floor