Download Chapter 2

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
 Atlantic
 Indian
 Artic: 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, bestknown layer
• Thin
• Floats on Mantle
Two Types of Plates Make Up the Earth’s Crust
Composition
Continental
Granite
Oceanic
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 MidOcean
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???
Magma pushes through the midocean ridge
2. Magma cools to form new sea
floor
3. As more magma pushes through,
the sea floor spreads out—
SEA-FLOOR SPREADING
1.
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 Collisions
 Oceanic-
Oceanic
 Trenches
(deep cracks
in the crust)
are formed.
Types of Collisions
 Continental-
Oceanic
 Trenches
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
Continental Margins
(Boundaries between continents)
The Continental Shelf
(Submerged part of the continent)
The Continental Slope
(Actual edge of the continent)
The Continental Rise
(Where continental
sediments are deposited)
*Most marine life
*Best fishing
*1km-750m long
*Part of continent that
begins to slope down
*3,000-5,000 m long
*Pieces of the continental
slope break off
and collect to form
the rise.
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