2. A. The Geography of the Ocean Basins
The oceans cover 71% of the planet and regulate its
climate and atmosphere
There are four ocean basins
Pacific – the deepest and largest
Atlantic
Indian
Arctic – smallest and shallowest
Connected to the main ocean basins are shallow seas
e.g. Mediterranean Sea, Gulf of Mexico, South China Sea
They all connect to form a world ocean where seawater,
materials, and organisms
can move about
3.
4. B. The Structure of the Earth
In the early molten Earth, lighter materials floated
toward the surface
They cooled to form the crust
The atmosphere and oceans then formed
Earth is the right distance from the sun for liquid water,
and life, to exist
1. Internal Structure
The dense core is mostly iron
Solid inner core and liquid outer core
The swirling motions produce the Earth’s magnetic field
The mantle is outside the core and under the crust
Near molten rock slowly flows like a liquid
The crust is the outer layer, comparatively thin
Like a skin floating on the mantle
5.
6. 2. Continental and Oceanic Crusts
There are differences in the crust that make up sea floors
and continents
a. Ocean crust
Made of basalt – a dark mineral
More dense
Thinner
Younger rock; 200 mil years
b. Continental crust
Made of granite – lighter color
Less dense
Thicker
Older rock; 3.8 bil years
So continental crust floats high on the mantle and ocean
crust floats lower
That’s why ocean crust is covered by water
7. The Origin and Structure of the Ocean Basins
The Earth is a world of constant transformation, where
even the continents move
A. Early Evidence of Continental Drift
400 years ago Sir Francis Bacon noted the continental
coasts of the Atlantic fit
together like pieces of a puzzle
Later suggested the Americas might have been once
joined to Europe and Africa
Geologic formations and fossils matched from opposing
sides
Alfred Wegner gave hypothesis of Continental Drift in
1912
Suggested that all the continents had once been a
supercontinent, named
Pangea
Started breaking up ~180 mil years ago
8. B. The Theory of Plate Tectonics
Could not explain how the continents moved
The Theory of Plate Tectonics explains it all
Continents do drift slowly around the world
9. Discovery of the Mid-Ocean Ridge
After WWII sonar allowed detailed maps of the
sea floor
They discovered the mid-ocean ridge system
A chain of submarine volcanic mountains
that encircle the globe, like seams on a
baseball
The largest geological feature on Earth
Some of the mountains rise above sea level to form
islands, e.g. Iceland
The mid-Atlantic ridge runs down the center of the
Atlantic Ocean and follows
the curve of the opposing coastlines
Sonar also discovered deep trenches
10. Significance of the Mid-Ocean Ridge
Why are they there? How were they formed?
Lots of seismic and volcanic activity around
the ridges and trenches
Rock near the ridge is young and gets older
moving away from the ridge
There is little sediment near the ridge, but it
gets thicker moving away
Found symmetric magnetic bands on either side of
the ridge which alternate normal and reversed
magnetism
11.
12. Creation of the Sea Floor
Huge pieces of oceanic crust are separating at the
mid-ocean ridges
Creating cracks called rifts
Magma from the mantle rises through the rift
forming the ridge
The sea floor moves away from the ridge
This continuous process is called sea-floor spreading
New sea floor is created
This explains why rocks are older and sediment is
thicker as you move away from
the ridge
This also explains the magnetic stripes found in the
sea floor
13.
14. Sea-Floor Spreading and Plate Tectonics
The crust and part of the upper mantle form the
lithosphere
100 km (60 mi) thick, rigid
It’s broken into plates
May be ocean crust, continent crust, or both
The plates float on a fluid layer of the upper mantle called
the asthenosphere.
At mid-ocean ridges the plates move apart
If the plate has continental crust it carries the continent
with it
Spread 2-18 cm/year
This explains continental drift
15.
16. As new lithosphere is created, old lithosphere is destroyed
somewhere else
Some plate boundaries are trenches where one plate sinks
below the other back down into the mantle and melts
Called subduction
Trenches are also called subduction zones
The plates colliding can be ocean - continent
¨ Ocean plates always sinks below
¨ Produces earthquakes and volcanic mountain
ranges; e.g. Sierra Nevada
The plates colliding can be ocean - ocean
¨ Earthquakes and volcanic island arcs; e.g. Aleutian
Islands
The plates colliding can be cont - cont
¨ Neither plate sinks, instead they buckle
¨ Producing huge mountain ranges; e.g. Himalayas
17.
18. A third boundary type
is shear boundary
or transform fault
The plates slide past
each other
Causes earthquakes;
e.g. San Andreas Fault
Two forces move the
plates
Slab-Pull theory - the
sinking plate pulls the
rest behind it
Convection theory –
the swirling mantle
moves the plate
19.
20. C. Geologic History of the Earth
Continental Drift and the Changing Oceans
200 mil years ago all the continents were joined in
Pangea
It was surrounded by a single ocean called
Panthalassa
180 mil years ago a rift formed splitting it into two
large continents
Laurasia – North America and Eurasia
Gondwana – South America, Africa, Antarctica, India,
and
Australia
The plates are still moving today
Atlantic ocean is growing, Pacific is shrinking
21.
22. The Record in the Sediments
Two types of marine sediments:
Lithogenous – from the weathering of rock on land
Biogenous – from skeletons and shells of marine
organisms
¨ Mostly composed of calcium carbonate or silica
Microfossils tell what organisms lived and past ocean
temperatures
Climate and Changes in Sea Level
The Earth alternates between interglacial (warm) period
and ice age (cold) periods
Sea level falls during ice ages because water is trapped in
glaciers on the
continents
23. The Geological Provinces of the Ocean
Two main regions of the sea floor
Continental margins – the submerged edge of the
continents
Deep-sea floor
A. Continental Margins
Boundaries between the continental and ocean crust
Consists of shelf, slope and rise
The Continental Shelf
The shallowest part
Only 8% of the sea floor, but biologically rich
and diverse
Large submarine canyons can be found here
Ends at the shelf break, where it steeply slopes down
24.
25. The Continental Slope
The edge of the continent
Slopes down from the shelf break to the deep-sea
floor
The Continental Rise
Sediment accumulates on the sea floor at the base of
the slope
Active and Passive Margins
Active margin – the subducting plate creates a trench
Narrow shelf, steep slope, and little or no rise
Steep, rocky shorelines
Passive margin – no plate boundary
Wide shelf, gradual slope, and thick rise
26.
27. Deep-Ocean Basins
10,000-16,000 ft
Abyssal plain - flat region of the sea floor
Seamounts – submarine volcanoes
Guyots – flat-topped seamounts
Both were once islands, but now covered with water
Trenches – the deepest part of the ocean
Mariana Trench is 36,163 ft deep
28. The Mid-Ocean Ridge and Hydrothermal Vents
At the center of the ridge, where the plates pull apart, is
a central rift valley
Water seeps down through cracks, gets heated by the
mantle, then emerges through hydrothermal vents
350oC (660oF)
Dissolved minerals from the mantle, like sulfides, are
brought up
Black smokers form when minerals solidify
around a vent
Marine life, including chemosynthesizers, exist
around hydrothermal vents
