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