1. The Sea Floor
Chapter 2

2. The Water Planet · Habitats are shaped by geological processes
o  Form of coastlines
o  Depth
o Type of bottom – sandy, muddy, rocky

3. The Water Planet · Earth has lots of liquid water
 Most other planets have little water
 Oceans play major role in weather
 Without water life would not be possible
 71% of the earth is covered by water
2/3 of the land on earth is found in the Northern Hemisphere

4. 4 Major Ocean Basins
  Pacific – deepest and largest (as big as the others combined)
Atlantic – larger than Indian
Indian - similar depths to Atlantic
Arctic – smallest, shallowest

5. The World’s Oceans

6. World Ocean · The oceans are interconnected – not separate
· The connections allow sea water, materials, and some organisms to move from one to another

7. EARTH MATERIALS
A mineral is a natural inorganic solid with an orderly arrangement of atoms and fixed physical and chemical properties
Rocks are classified based on the conditions in which they formed
Igneous rock is cooled and crystallized magma
Sedimentary rock is composed of compacted organic and inorganic material
Metamorphic rock is derived from other rocks via high pressure, intense heat and chemical transformation
© AMS

8. Minerals · Oceanic crust – minerals called basalt
·       Continental – granite
·       Oceanic crust is denser
·       Oldest oceanic rocks are less than 200 million years old
* Continental rocks – up to 3.8 billion years

9. Oceanic Crust and Continental Crust
ROCK CYCLE
Surface and internal geological processes that transform rock from one type to another
Rocks and component minerals are continually regenerated
Regeneration of rocks and minerals may take many millions of years
In the time frame of a human lifetime or even of civilization, the rate of regeneration of rock, is so slow that for all practical purposes the supply is fixed and finite
© AMS

10. © AMS
The Rock Cycle

11. CONTINENTAL MARGINS
Three distinct zones seaward from the coastline based on water depth
Continental shelf: initial, gently sloping zone
Continental slope: more steeply sloping zone
Continental rise: transitional region
The continental shelf, slope, and rise together comprise the continental margin
Sediment spreads over the ocean floor forming vast, flat abyssal plains seaward of the continental rise
© AMS

12. Ocean Bottom Profile
Cross-sectional profile of the continental margin and ocean bottom with the vertical scale greatly exaggerated.
© AMS

13. Continental Drift 1620 Francis Bacon
Noted the continents fit together like pieces of a puzzle
Coal deposits and other geological formations match up on opposite sides of the Atlantic
Fossil evidence also supports this idea

14. Continental Drift Alfred Wegener – proposed “continental drift” Pangea
proposed that all the continents were once joined in a single “supercontinent”
 Pangea
  Started breaking up 180 million years ago

15. Plate Tectonics and Ocean Basin Features
Divergent, convergent and transform boundaries of major lithosphere plates.
© AMS

16. Pangea

18. Plate Tectonics · What causes the continents to drift?
A process called plate tectonics

19. Mid Ocean Ridge · Sonar surveys revealed a mid ocean ridge system
Continuous chain of volcanic submarine mountains that circle the earth
Largest geological system on the planet
At regular intervals – transform faults
Sometimes the ridges are so high they break the surface like iceland
Mid-Atlantic Ridge – runs down the middle of the Atlantic Ocean

20. Ridges

21. Ridges & Trenches Great deal of activity around the ridges
Earthquakes around the ridges
Volcanoes at the trenches
Scientists found that the farther you get from the ridge, the thicker the sediments get and the older the rocks

22. The largest circles denote the strongest earthquakes.
Most geological activity occurs along the boundaries of major lithosphere plates.
Yellow lines represent plate boundaries and yellow triangles active volcanoes.
Earthquakes are represented by circles, colored according to depth (red: 0-69 km, green: km, blue: km).
The largest circles denote the strongest earthquakes.
© AMS

23. Earth’s Magnetic Field
The earth’s magnetic field reverses a few times every million years
During the shift, a compass would point to the magnetic “north” – that is what is now the south pole. 
Cause of the reversals is unknown, but thought to be related to changes in movement of material in the outer core

24. Magnetic Anomolies
Many rocks are magnetic. If they are in the molten outer core, they are free to point to magnetic north
When the rocks cool, they stay in the same position
Geologists found a pattern of magnetic stripes or bands in the mid ocean ridge system.
Symmetrical around the ridge – mirror images
The magnetic bands are called “magnetic anomalies”

27. A – 5 mya B – 3 mya C- present day

28. Ocean formation Ocean formation at a divergent plate boundary
MARN 1002 Introduction to Oceanography
Ocean formation
Ocean formation at a divergent plate boundary
Ocean grows wider as new oceanic crust is formed along the mid- ocean ridge and seafloor spreading continues

29. What did that show?
Shows the sea floor was not formed all at once, but in strips along the mid-ocean ridge

30. Creation of the Sea Floor
·  Magnetic anomalies together with other evidence led to the understanding of plate tectonics
· At the ridges, large pieces are separating 
· As the pieces separate, they form a crack or “rift”
· This releases pressure and some material rises through the rift
· The ascending material pushes up and forms a ridge
·       The process is called sea-floor spreading

31. Sea Floor Spreading and Plate Tectonics
Lithosphere – “Rock Sphere”
Broken into plates called lithospheric plates

32. Plates · The plates are about 100 km thick
·  Plates contain oceanic crust, continental crust or both
The Mid-Ocean Ridges form the edges of many of the plates

33. How Fast Do They Move?
· The plates move at between 2 and 18 cm per year
· Human fingernails grow at 6 cm per year

34. Subduction
· As lithosphere is created at the ridges, it must be destroyed somewhere else 
· It is destroyed at the trenches 
· Trenches are formed when 2 plates collide and one sinks below the other
· The downward movement is called subduction 
· Trenches are sometimes called “subduction zones”

35. The Mid-Atlantic Ridge occurs where adjacent plates diverge and is part of a lengthy ridge system that winds through the ocean basins.
© AMS

36. HYDROTHERMAL VENTS
Near divergent plate boundaries, water circulates through rock fractures in the seafloor and discharges through hydrothermal vents
Cold seawater is superheated by shallow volcanic activity
Dissolves minerals in crustal rock
Mineral-rich water ejects out through vents
© AMS

37. HYDROTHERMAL VENTS
Precipitates appear as clouds (black or white smokers)
Accumulate as conical chimneys more than 10 m tall
Home to diverse communities of exotic marine organisms, including bacteria, crabs, shrimp, mussels, starfish, and tubeworms
© AMS

38. Spreading and Closing Cycles
Wilson cycles
Cycle of ocean basins expanding then contracting as new supercontinents
May take 500 to 600 million years
Embryonic stage:
Underlying mantle warms and expands, elevating the overlying continent and stretching the continental crust
Example: African continent
Juvenile stage
With rifting, broken sides rise and create a valley that often fills with fresh water
Rift valleys continue to widen until reaching the ocean, transforming the freshwater lake into a saline gulf
Example: Red Sea and Gulf of California
Mature stage
Divergent plate boundary widens and additional oceanic crust is generated
Example: Atlantic Ocean
© AMS

39. Spreading and Closing Cycles
Declining stage
Subduction becomes widespread around the border of the ocean basin
Example: Pacific Ocean (Ring of Fire)
Terminal stage
Ocean basin closes through subduction, continents from opposite sides draw closer and but still have a narrow sea between
Example: African and European continents with Mediterranean Sea between
Suturing stage
Collision of the continents is complete; sea is gone and continents override each other causting uplift and mountain building
Example: Indian and Eurasian plates with Himalayan Mountains
© AMS

40. A simplified model of the Wilson cycle, showing the formation and closing of an ocean basin.
© AMS

41. ???
Oceanic plate always descends into the mantle when colliding with a continental plate. Why?

42. Because the continental plate is less dense
Answer
Because the continental plate is less dense

43. Sediment source Table 4.5 summarizes sediment sources:
MARN 1002 Introduction to Oceanography
Table 4.5 summarizes sediment sources:
Lithogenous: pre-existing rocks (terrigenous)
Biogenous: from marine organisms
Hydrogenous: precipitated from seawater
Cosmogenous: from outer space
MARN Introduction to Oceanography

44. A Record in the Marine Sediments
·       2 major types of sediments are found in the sea.
Lithogenous sediment
- Physical and chemical breakdown or weathering of rock
Biogenous Sediment
   Skeletons and shells of marine organisms
 Calcium carbonate – calcareous ooze
 Silica – siliceous ooze