Download U4-T1.1-Wegeners Continental Drift Theory

Earth Systems 3209
Unit: 4
The Forces Within Earth
Reference:
Chapters 4, 15, 16, 19; Appendix A & B
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Unit 4:
Topic 1.1
Theory of Continental Drift
Focus on . . .
 describing the theory of continental drift as proposed by
Alfred Wegener.
 discussing the ideas provided by both Alfred Wegener
and Arthur Holmes explaining the mechanism behind
continental movement.
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Theory of Continental Drift
Some earlier ideas of continental drift include:
 Rodinia is one of many different supercontinents that is
believed to have existed before Pangaea.
 An early theory believed that continents simply ‘drifted’
through the ocean floor pushing up material in front,
forming mountain belts. However, this theory lacked a
valid mechanism for driving the process behind
continental movement .
 Many of the earlier theories had trouble explaining the
process of why the continents moved ….
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Theory of Continental Drift
 A German scientist, named Alfred Wegener was
one of the first scientist to propose that
continents had once been closer together.
 Wegener called this idea “Continental Drift.” His
idea was not widely accepted because scientist
believed that the continents and oceans were
permanent features fixed in their position and
did not move.
Text Reference:
Pages 514-515
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Theory of Continental Drift
 Wegener’s idea was:
 Hundreds of millions of years ago, a supercontinent called,
“Pangaea” once existed. At approximately 200 million
years ago, this landmass split into smaller pieces and
drifted apart reaching their present day positions.
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Theory of Continental Drift
 Wegener’s main criticism centered around why the continents move.
 A weakness in Wegener’s theory was it could not satisfactorily
answer the question asked by critics:
Q: What kind of forces could be strong enough to move such large
masses of solid rock over such great distances?

In 1915, Wegener suggested that the continents plow through the
oceans as a snow plow would trough snow. He also believed that
the Earth’s rotation and the moon’s gravitational forces were
responsible for the drifting of continents. This reasoning for the
movement of continents was not widely accepted since most
scientists still believed the Earth was a solid, motionless body.
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Theory of Continental Drift
 Main Points of Continental Drift Theory Include:
1) 225 Million years ago, supercontinent called Pangaea.
2) 200 Million years ago, supercontinent split to form two
main land masses. Laurasia in the north and
Gondwanaland in the south.
3) Laurasia consisted of; Asia, Europe, and North America.
4) Gondwanaland consisted of; Africa, Australia, Antarctica,
South America, and India.
5) Over the past 150 million years, these land masses split
and drifted to their present positions.
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Theory of Continental Drift
 After Wegener’s death in 1930, much evidence was
discovered to support the Continental Drift Theory.
 However, at the time that Wegener proposed his theory of
continental drift, most scientists still believed the Earth was
a solid, motionless body.
 Majority of this evidence was discovered during ocean floor
exploration and the question Wegener failed to answer was
explained by a scientist named Arthur Holmes.
 Holmes speculated that the circular motion of the mantle
carried the continents along in much the same way as a
conveyor belt.
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Theory of Continental Drift
 Holmes suggested that continents and the
ocean floor move primarily due to forces in the
asthenosphere (upper mantle) which causes
material to move as convection cells.
 Mantle material moves up at ridges and move
away in opposite directions moving the
continents. In cooler areas beneath trenches,
mantle material sinks causing oceanic crust to
descend into the mantle and be recycled.
 This idea was first considered in the 1930s by
Arthur Holmes, the English geologist who later
influenced Harry Hess' thinking about seafloor
spreading.
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Example 1:
Which scientist proposed the existence of a
supercontinent called Pangaea?
(A) Alfred Wegener
(B) Arthur Holmes
(C) Harry Hess
(D) Tuzo Wilson
Which is the name of the supercontinent that
existed before Pangaea?
(A) Gondwanaland
(B) Iapetus
(C) Laurasia
(D) Rodinia
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Example 2:
Which is the most recent supercontinent?
(A) Appalachians
(B) Iapetus
(C) Pangaea
(D) Rodinia
Which Earth layer contains convection currents that
cause plate movement?
(A) asthenosphere
(B) inner core
(C) lithosphere
(D) outer core
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Your Turn . . .
Take the time and complete the following questions . . .
(Solutions to follow)
Question:
With reference to Rodinia and Pangea, use the
Plate Tectonics theory to describe what our
planet could look like in the future.
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Solutions . . .
Question:
With reference to Rodinia and Pangea, use the Plate Tectonics
theory to describe what our planet could look like in the future.
Answer:
In the past billion years scientist suggest that the major
landmasses of Earth joined together on numerous occasions to
form super continents, Rodinia and Pangaea are two such
examples. With undisputable evidence supporting a mobile
Earth which forms the basis of the plate tectonic theory, it is
believed that the major landmasses will once again in the future
join to form another massive super-continent.
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Summary . . .
Overview of Points covered:
 Alfred Wegener proposed the Continental Drift Theory.
 Wegener could not explain why the continents move!!
 Arthur Holmes proposed an acceptable “mechanism” to
explain Wegener's theory of continental drift.
 Holmes suggested that the movement of convection currents
in the Asthenosphere is responsible for moving the continents.
 Holmes ideas behind convection in the mantle later influenced
Harry Hess to propose the theory of seafloor spreading.
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