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Chapter 2
The Sea Floor
The Water Planet
OCEANS
Cover 71% of the globe
Regulate earth’s climate and atmosphere
The Geography of the Ocean Basins
Northern Hemisphere: 61% water
Southern Hemisphere: 80% water
Ocean Basins Four Ocean Basins
Pacific: Largest
AtlanticIndianArtic: Smallest
The Structure of the Earth
Earth = 4.5 Formed from the
Big Bang:cosmic explosion of dust
Occurred 13.7 billion years ago
Dust Particles kept colliding until planets formed.
Early Earth
Early earth was most-likely MOLTEN.
As earth cooled: Densest material flowed toward center of
earth. Lighter materials floated toward the
surface.
Earth Began to Cool As Earth Cooled: Atmosphere formed
Oceans formed
Internal Structure of Earth
Core inner-most layer
Composed of iron
Internal Structure of Earth
Mantle• Molten-solid
rock• Flows around
core like liquid
Internal Structure of Earth
Crust• Outermost,
best-known layer
• Thin• Floats on Mantle
Two Types of Plates Make Up the Earth’s Crust
Continental Oceanic
Composition Granite Basalt
Density Less Dense More Dense
Age (oldest rocks) 3.8 Billion Years Old
200 Million Years Old
Elevation Above Sea Level Below Sea Level
The Origin and Structure of Ocean Basins
THE EARTH IS IN A STATE OF CONSTANT TRANSFORMATION.
Early Evidence of Continental Drift Sir Thomas Bacon (1620): noticed
the coasts of continents fit together like puzzle pieces.
Alfred Wegener (1912): Proposed continental drift hypothesis.“All Continents were once joined”: PANGAEA
Pangea
The Theory of Plate Tectonics
Wegener’s hypothesis was not widely accepted because he could not explain HOW continental drift occurred.
The Theory of Plate Tectonics
1950s-1960s: Scientists had enough evidence to conclude that continents did “drift.”
PLATE TECTONICS
Discovery of the Mid-Ocean Ridge
Sonar lead to discovery during WW2
Continuous chain of volcanic mountains that encircle the globe
Significance of the Mid-Ocean Ridge
The Sea floor is created at the Mid-Ocean Ridge
Magnetism of Ocean Floor Rocks
BACKGROUND: Earth magnetic field reverses direction every few million years. Many rocks contain tiny magnetic particles & these move in molten rock. When the rock solidifies the particles freeze in their orientation
Geologists found patterns of magnetic bands or stripes in the sea floor running parallel to the mid-ocean ridge
The bands are symmetric around the ridge Magnetic bands = magnetic anomalies
How is the Sea-floor Created???
1. Magma pushes through the mid-ocean ridge
2. Magma cools to form new sea floor
3. As more magma pushes through, the sea floor spreads out—
SEA-FLOOR SPREADING
Sea-Floor Spreading & Plate Tectonics
Earth’s surface is broken into plates.Plates are made of crust and top layer of mantle: LITHOSPHERE
Plates spread 2-18 cm per year. (Fingernails grow 6 cm per year.)
Plate Movement
As plates move, they collide with other plates.
*USUALLY* Subduction Occurs: one plate
is forced into the mantle when 2 plates collide.
Types of CollisionsOceanic-
OceanicTrenches (deep cracks in the crust) are formed.
Types of Collisions
Continental-OceanicTrenches produced.
Types of Collisions
Continental-Continental: produces mountains.
Sliding Plates
Sometimes plates slide past each other
Faults are formed from this process
Earthquakes are produced from this process
What Makes Plates Move??? SLAB PULL:
oceanic crust becomes too heavy to float on the mantle and it sinks down into it, pulling the rest of the plate with it (slowly).
Geological History of the Earth
Continents were once united: PANGAEA
PANGAEA: began to break up 180 million years ago.
Geological Provinces of the Ocean
*M o st m arin e life*Best fi sh in g
*1km - 750 m lo n g
The Continental Shelf( Su bm erged part o f the co n t in en t)
*P art o f co n t in en t thatbegin s to slo pe do w n
*3,0 0 0 - 5,0 0 0 m lo n g
The Continental Slope( A ctu al edge o f the co n t in en t )
*P ieces o f the co n t in en talslo pe b reak o ff
an d co llect to fo rmthe r ise.
The Continental Rise( W here co n t in en tal
sed im en ts are depo sited )
Continental M argin s( Bo u n daries betw een co n t in en ts)
Types of Continental Margins
Active: Narrow shelves Steep Slopes Little or no rise
*Example: Pacific Coast of North America
Types of Continental Margins
Passive Wide shelves Gentle slopes Well-developed rise
*Example: Atlantic coast of North America
Deep Ocean Basins
Deep-sea floor (ABYSSAL PLAIN): average of 4,000 m deep (13,000 ft)
Features of the Deep-Sea Floor
Trenches :the deepest part of the ocean floor
Rift Zone: break in the earth’s crust from which lava flows and new seafloor forms.
Seamounts :submarine volcanoes Guyots: flat-topped volcanoes (INACTIVE) Abyssal Plain: flat part of seafloor Abyssal Hills : small hills Plateaus: flat-topped mountains
Guyots Flat-topped
seamounts
Trenches
Deepest parts of the ocean.
Deepest: 36,163 ft.
Mid-Ocean Ridge and Hydrothermal Vents
Central Rift Valley Located in center of
Mid-Oceanic Ridge where plates are pulling apart.
Hydrothermal Vents
Deep-sea hot springs
Formed when water that has been heated by the mantle forces its way through the earth’s crust
Black Smokers
Chimney-like structures
Build up around vents
Release “clouds” of minerals that have been heated by the vents