Transcript The Restless Continents

Have you ever looked at a map
of the world?
O Did you notice how the coastlines of
continents on opposite sides of the oceans
appear to fit together like the pieces of a
puzzle?
Is this a coincidence?
O How is it that the coastlines fit together so
well?
O Is it possible that the continents were
actually together sometime in the past?
Wegener’s Continental Drift
Hypothesis
O One Scientist who
looked at the pieces
of this puzzle was
Alfred Wegener in
the early 1900’s
O He wrote about his
hypothesis:
Continental Drift
Continental Drift
O The hypothesis that
the continents once
formed a single
landmass, broke up,
and drifted to their
present locations.
Continental Drift explained a
few puzzling questions
O Why do the continents seem
to fit together like a giant
puzzle?
O Why are fossils of the same
plant and animal species
found on continents that are
on different sides of the
Atlantic Ocean?
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Mesosaurus – SA, Africa
Glossopterous –Antartica,
Africa, Australia
O Why are rocks with different
magnetic alignments found in
the same place
(paleomagnetism)?
The Hypothesis
O Wegener made many
observations before
proposing his
hypothesis of
continental drift.
O He thought that all the
present continents
were once joined in a
single, huge continent
called Pangaea
Pangaea
O “Pangaea” means “all
O
O
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earth”
It existed about 245
million years ago
It split into two huge
continents about 180
million years ago
Laurasia
Gondwana
These two continents split
again about 65 million
years ago to form the
continents we know today
But Wegener’s theory of continental
drift was not widely accepted during
his lifetime….
O Many scientists would not accept his
hypothesis.
O They said that the calculated strength of the
rocks that make up the Earth’s crust would
not allow the crust to move in that way.
O Many years later, other evidences were
presented that supported his theory.
What do you think…
O Our continents will look like in the future?
O Will we move back together?
O Will we be further apart?
O What evidence will future scientists use to
show our current day locations?
Demonstration of Sea Floor
Spreading
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Fold your 1 meter of paper in half to
form a “V”
Slide the paper between two tables.
Have them close enough to grip the
paper, but far enough apart so that
the paper can slide through the
crack.
Using the ruler, slide the paper out
10 cm one each side.
Draw a vertical line on the paper at
the table’s crack. Label this area
“1” on both sides of the paper
Measure out 10 more cm, draw your
line and label this area “2”on both
sides of the paper
Continue this until you have 5
sections on each side
The Restless Planet:
Sea Floor Spreading
Unit 2: Sixth Grade
So what did Wegener believe
was moving the continents?
O Sea-floor Spreading !
O It was proposed that as the tectonic plates
move apart, it creates a rift that allows magma
to rise to the surface of the ocean floor and
solidifies.
O Mid-Ocean ridges are places where sea-floor
spreading takes place
O Mid-Atlantic Ridge
O This creates new crust in that area, further
pushing the continents apart.
O Evidence: older crust is farther away from the
mid-ocean ridge than newer crust is.
Sea-Floor Spreading
http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=related&safety_m
ode=true&persist_safety_mode=1
Mid-Atlantic Ridge
Debate
O We will be debating the most compelling evidence to
support the theory of continental drift.
O There will be three groups.
O Group 1: Fossil Similarities
O Group 2: Landform Similarities
O Group 3: Sea Floor Spreading
O You will have 20 minutes to form your argument.
O Use notes, ITs, netbooks to find info
O Write your points on the construction paper as
bullets
O Groups will then present their arguments to the class
Other evidence to support
continental drift
O Stratigraphy: studying the layers of the
Earth, showed that the geologic columns in
Antarctica and India were similar
O Glaciation: Glacial deposits in Canada were
also found in India and southern Africa
O Marine Corals
O Mountain Belts: ancient mountains in South
Africa and near Buenos Aires, Argentina
align when the two continents are fitted
together.
More evidence to support SeaFloor Spreading
O Magnetic Reversals
O Throughout Earth’s history, the north and south
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poles have changed places many times.
The molten rock at the mid-ocean ridges contains tiny
grains of magnetic minerals.
They act as compasses, lining up with the magnetic
field of the Earth.
When the magma cools, these tiny compasses are
preserved in the rock.
When the poles reverse, the mineral grains are
aligned in with the “incorrect” pole.
Paleomagetism
Magnetic Reversals