Transcript File

DYNAMIC EARTH
CONTINENTAL DRIFT HYPOTHESIS
• Alfred Wegner in 1915
proposed a hypothesis
of CONTINENTAL DRIFT.
• The continents formed a
single supercontinent
called Pangaea
PANGAEA
CONTINENTAL DRIFT
• Pangaea broke apart
into 2 continents
Gondwanaland and
Laurasia about 200
million years ago.
• Scientists propose that
the continents are
drifting apart today at
a rate of 2.54 cm/year.
(Rate that your
fingernail grows)
CONTINENTAL DRIFT
• continental drift
• What do you think the continents will look like in 250 million
years from now?
EVIDENCE FOR CONTINENTAL DRIFT
Continents fitting together like a
puzzle.
Rock Types
Ancient Climates
Matching Fossils
PUZZLE PIECES
• What could be some
reasons these continents
don’t match up
perfectly?
• What might the brown stuff
be?
• How about the light blue?
ROCK TYPES
• The Appalachian Mountains that run along North
America are similar in age and structure as the
mountains found in the British Isles and Scandinavia.
ANCIENT CLIMATES
• Wegner found glacial deposits that date back to
220 – 300 million years ago.
• Deposits were discovered in locations that have
tropical climates today.
• Wegner suggested that during this same time
period, large tropical swamps existed in the
Northern Hemisphere.
• This is how we have major coal fields in the Eastern United
States, Europe, and Siberia
ANCIENT CLIMATE
FOSSIL EVIDENCE
• Fossil evidence for continental drift
includes several fossil organisms
found on different landmasses.
• Glossopteris
• Small plant found in South America,
Southern Africa, and India
• Seeds were not likely to travel over oceans
(long distances) to different continents.
• Mesosaurus
• Found in South American and Southern
Africa
• Lived in freshwater lakes and shallow bays
• Not likely to be able to swim across the salty
Atlantic Ocean
FOSSIL EVIDENCE ACTIVITY
• Students will label the continents
• Students will color in different fossils and continents
on paper and create a key for the fossils.
• Carefully cut each continent out on the bolded line
(continental shelf).
• On a separate sheet of paper glue the continents
so they fit together and the fossils match up.
• On the back of your paper write a brief explanation of why
there may be areas that don’t match up perfectly.
• There could be areas of overlap or areas that don’t meet up.
CHECKPOINT
• What are the 4 pieces of evidence Alfred Wegner
used for his continental drift theory?
• TEXT POLL
FOSSIL EVIDENCE ACTIVITY
Key for Evidence
REJECTION OF THE HYPOTHESIS
• Alfred Wegner could not explain what made the
continents move.
• After the science world rejected him they started
exploring the idea more.
• More technology became available and they
found more evidence to support Wegner’s theory.
• In 1967, the new evidence that was found led to a
new theory called PLATE TECTONICS THEORY.
EXPLORING THE OCEAN FLOOR
• Scientists started to
explore the topography of
ocean floor.
• In the early 1900s a new
technology was discovered
called SONAR (SOund
NAvigation and Ranging)
• Uses sound waves to calculate
the distance to an object.
MAIN OCEAN FEATURES
• Deep-Ocean Trench
• Form the deepest parts of the ocean.
• Most occur along the edges of the Pacific Ocean.
• Ex. Marianas Trench in the Pacific Ocean
• Mid-Ocean Ridges
• A long chain of mountains that extend the length of the
Ocean.
• Longest feature on Earth’s surface.
• 70,000 km (43,496 miles) through all the major ocean basins
• 1,000-4,000km (621-2,485 miles) wide
• Rift Valley
• The central valley of a mid-ocean ridge
• Resembles a Canyon
RIDGES OF THE OCEANS
CHECKPOINT
• What is the technology used to measure the depth
of the ocean?
•
•
•
•
A. GLOMAR
B. SAMSUNG
C. SONAR
D. RIDGES
CONTINENTAL MARGIN
• Continental margin – area of transition between continent
and ocean basin floor.
• Continental Shelf – part of the continent that is under shallow
water (up to 130 meters deep).
• Continental Slope – begins at the shelf edge, where depth
falls off rapidly; the boundary between the continental crust
and oceanic crust.
CONTINENTAL MARGIN (CONT)
• Continental Rise – Formed of
thick sediment deposits.
• Submarine Canyon – deep
V-shaped valleys cut into
the continental shelf and
slope.
• Turbidity current –
movement of thick
sediment down the
continental slope.
• Cause of Submarine canyons
• Can be disturbed by an
earthquake
CONTINENTAL MARGIN
OTHER SEA-FLOOR FEATURES
• Abyssal plains – large flat areas of the ocean floor formed of
thick sediments.
• Seamount – cone shaped mountain peaks that rise high
above the deep ocean floor; may be above or below sea
level.
• Tablemount (Guyot)– flat-topped seamount; formed by
wave erosion; may be above or below sea level.
OTHER SEA-FLOOR FEATURES
MARIANA
TRENCH
• Deepest part of the Earth’s crust
• Scientists Jacques Piccard and Don Walsh
• Mariana Trench Activity
SEA-FLOOR SPREADING
• Harry Hess in 1963
came up with a
Hypothesis: Sea-Floor
Spreading
• New ocean floor forms
along Earth’s midocean ridges,
• Slowly moves outward
across ocean basins
causing the spreading.
SEA-FLOOR SPREADING
• As the seafloor spreads our planet is not getting
larger so we have to make up for this with
SUBDUCTION.
• When the ocean floor returns to the mantle via the deep
trenches.
• The oldest rocks are being pushed into the trenches
and eventually are re-melted back into magma.
• Rate of seafloor spreading is about 5 cm/year
SEA-FLOOR SPREADING
Mid-ocean Ridge
Trench
Lithosphere
Subduction of
ocean floor
Asthenosphere
EVIDENCE FOR SEA-FLOOR SPREADING
Paleomagnetism
Earthquake Patterns
Ages of the ocean-floor
rocks
PALEOMAGNETISM
• The study of changes in Earth’s magnetic field.
Shown by patterns of magnetism in rocks that have
formed over time.
Normal Polarity- When
rocks show the same
magnetism as the
present magnetism
field.
Reverse Polarity- When
rocks show the
opposite magnetism as
the present magnetism
field.
POLARITY OF THE OCEAN CRUST
• The discovery of strips of alternating polarity, which
lie as mirror images across the ocean ridges, is
among the strongest evidence of seafloor
spreading.
EARTHQUAKE PATTERNS
• Scientists found a relationship between deep-focus
earthquakes and ocean trenches.
AGE OF THE OCEAN FLOOR
• In 1968, the ship Glomar Challenger collected data
from both sides of mid-ocean ridges from deep sea
drilling.
They found that
younger rocks
were closest to the
ridges and older
rocks were near
the subduction
zones.
CHECKPOINT
• Which scientist proposed a theory called Sea-Floor
Spreading?
• A. Alfred Wegner
• B. Harry Hess
• C. Jacques Piccard
LAYERS OF THE EARTH
LAYERS OF THE EARTH
Layer
State of
Matter
Crust
Solid
Mantle
Plastic
Outer Core
Inner Core
Temperature
Thickness
Composition
5-70 km (3-44
mi)
Oxygen
Silicon
870 °C
2,890 km (1796
mi)
Oxygen
Silicon
Magnesium
Liquid
2,200 °C
2,260 km (1404
mi)
Iron
Nickel
Solid
5,000 °C
1,220 km (758
mi)
Iron Nickel
• The LITHOSPHERE is made up of the rigid crust and the
upper solid part of the mantle.
• The ASTHENOSPHERE is the plastic part of the mantle.
• The Lithosphere floats on the Asthenosphere.
CHECKPOINT
• What is the difference between
the lithosphere and the
asthenosphere?
PLATE TECTONIC THEORY
Plate Tectonics is the theory that the Earth’s outer layer (crust)
is made up of plates, which have moved throughout history.
PLATE BOUNDARIES
Divergent Boundaries
Convergent Boundaries
• Oceanic-Oceanic
• Oceanic-Continental
• Continental-Continental
Transform Boundaries
DIVERGENT BOUNDARY
• Plate Movement: Away
from each other
• Result: New sea-floor is
created from Mid-Ocean
Ridges and there is volcanic
activity
• Example: Mid-Atlantic Ridge
OCEANIC-OCEANIC
CONVERGENT BOUNDARY
• Plate Movement: moving
toward each other.
• A subduction zone (Trench)
is formed
• Result: Volcanic Island
Arc
• Example: Aleutian Islands
OCEANIC-CONTINENTAL
CONVERGENT BOUNDARY
• Plate Movement: Moving
toward each other
• Subduction zones (Trenches)
are formed.
• Result: A mountain chain
with volcanoes
• Example: Andes Mountain
Range
CONTINENTAL-CONTINENTAL
CONVERGENT BOUNDARY
• Plate Movement: Moving
towards each other.
• When the plates collide they will
be folded.
• Result: A mountain Range
• Example: The Himalayas.
TRANSFORM BOUNDARY
• Plate Movement: Slide
horizontally past one
another.
• Result: Long Faults
• Example: San Andres Fault
CHECKPOINT
• When plates are moving away from each other
what type of boundary is it called?
• A. Convergent
• B. Divergent
• C. Transform
• Plate Animation
North
American
Plate
South
Nazca
American
Plate
Eurasian
Plate
African
Plate
Indian
Plate
Pacific
Plate
Australian
Plate
Plate
Antarctica
Plate
PLATE MOVEMENT
• Convection currents in the mantle.
• Heat from Earth’s inner and outer cores is
transferred through the mantle by convection.
• Hot magma rises at the mid-ocean ridge.
• Convection current moves away from the ridge dragging
the lithospheric plate with it.
• Cooler, denser rocks of the plate subduct (sink) into the
trench and back to the mantle.
CONVECTION CURRENTS
Convection Current
HOT SPOTS
• Areas in the middle of plates where magma
rises through the sea floor.
Example: Hawaiian
Islands.
As the Volcanoes move
off the hot spot they are
no longer active.
HOT SPOTS