1. The Water Planet

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

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

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

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

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

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

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

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

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

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

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