How Do Natural Forces
Change & Shape Our Planet?
LAYERS OF OUR PLANET
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PHYSICAL LAYERS
LITHOSPHERE (SOLID)
ASTHENOSPHERE
(LIQUID)
MESOSPHERE (SOLID)
OUTER CORE (LIQUID)
INNER CORE (SOLID)
CHEMICAL LAYERS
CRUST (Si + O)
MANTLE (Si)
CORE (Fe +Ni)
WHAT IS CONTINENTAL DRIFT?
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ALL LANDMASSES WERE ONCE ONE LARGE
SUPERCONTINENT CALLED PANGEA
HYPOTHESIZED BY ALFRED WEGENER IN 1915
Pangaea began spreading 200 million years ago
PROOF OF CONTINENTAL DRIFT
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CONTINENTS FIT LIKE PUZZLE PIECES
ROCK EVIDENCE
FOSSIL EVIDENCE
CLIMATIC EVIDENCE
WAS WEGENER’S HYPOTHESIS
ACCEPTED?
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HOW DO THE CONTINENTS
MOVE?
WEGENER PROPOSED THE
EARTH’S ROTATION
HOW COME THE OCEAN
BASINS AREN’T WORN
DOWN BUT THE
CONTINENTS ARE?
HOW IS THE SEA FLOOR
SPREADING?
HARRY HESS DURING WWII DISCOVERED THE
CRACK IN MID ATLANTIC RIDGE
 IS THE PLANET GROWING?
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What proof is there that the sea
floor is spreading?
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In the late 1950's, scientists mapped the present-day
magnetic field generated by rocks on the floor of the Pacific
Ocean.
The volcanic rocks which make up the sea floor have
magnetization because, as they cool, magnetic minerals
within the rock align to the Earth's magnetic field
A hypothesis was presented in 1963 by Fred Vine and Drummond Matthews to explain
this pattern. They proposed that lava erupted at different times along the rift at the crest of
the mid-ocean ridges preserved different magnetic anomalies.
Let’s make a model!
HOW PLATE TECTONICS TIES IT
ALL TOGETHER
Convergent Boundaries
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Converging Plates
destroy crust
During collisions
between two
continental plates,
large mountain
ranges, such as the
Himalayas are formed.
Volcanoes are usually
formed by converging
plates
Diverging Boundaries
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Divergent boundaries create
crust
Divergent boundaries within
continents initially produce
rifts which produce rift
valleys.
Divergent boundaries also
form volcanic islands which
occur when the plates move
apart to produce gaps which
molten lava rises to fill.
Thus creating a shield
volcano which would
eventually build up to become
a volcanic island.
Transform Boundaries
Neither creates or destroys crust
 Earthquakes occur along boundaries
 San Andreas (California) Fault created
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WHERE CAN WE FIND
EARTHQUAKES & VOLCANOS?
HOW DO WE CLASSIFY
VOLCANOS?
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Shield volcanoes, the largest
of the three types, are
gently sloping and built
almost entirely of low
viscosity basaltic lava flows.
The eruptions are generally
nonexplosive due to the low
silica content.
Shield volcanoes are typified
by those on the Hawaiian
and Galapagos Islands and
on Iceland.
CINDER CONE VOLCANOS
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Volcanic Cinder
Cone are formed by
highly viscous
rhyolitic magma
(approximately 70%
silica).
Volcanic domes are
typically small.
Big Southern Butte
and East Butte on the
Snake River Plain are
two excellent
examples.
COMPOSITE (STRATO) VOLCANOS
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Composite volcanoes are the most beautiful - - - and !
- - - the most deadly of the volcano types.
Their lovely steep-sided, symmetrical cone shapes are
built up by eruptions of intermediate viscosity andesitic
lava and explosive tephra.
Examples of composite volcanoes, also called
stratovolcanoes, are Mount St. Helens in Washingon and
Mount Fuji in Japan.
What causes rocks to melt into magma?
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Temperature
Pressure: As pressure increases the temperature
at which a rock will melt also increases
Water: A wet rock or mineral will melt at a lower
temperature
Types of Magma
TYPE
VISCOSITY
GAS
CONTENT
BASALTIC
LOW
1-2%
50%
Least
ANDESITIC MEDIUM
3-4%
60%
Medium
RHYOLITIC
4-6%
70%
Greatest
HIGH
SILICA
CONTENT
EXPLOSIVE
NESS
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VISCOSITY: Internal resistance to flow
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TEPHRA: Rock fragments that are thrown into the air
during a volcanic eruption
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PYROCLASTIC FLOW: Swift moving, potentially deadly
clouds of gas, ash and other volcanic material a violent
eruption gives off
How were the Hawaiian Islands
Formed?
WHAT IS WEATHERING?
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Physical: breaking
down of rock (rock
stays same)
Temperature
Ice
Plants & animals
Water
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Chemical: breaking
down of rock (rock
changes)
Oxidation
Plants
Carbonation
Acids
Water
WHAT IS EROSION?
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Picking up of rock and moving
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WATER
WIND
ICE/GLACIERS
GRAVITY
WHAT IS DEPOSITION?
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Depositing of rocks