On the Move:
Continental Drift and Plate Tectonic
By Jim Cornish
apart to
f o r m
t h e
continents as they
exist today.
(1) Have
you noticed that
South America and
Africa look like they
could fit together like
pieces in a jigsaw puzzle? If
you have, you are not alone. It was
first observed by the English writer
and scientist Sir Francis Bacon in the
17th century. In 1910, German
meteorologist Alfred Wegener saw it
too and developed a theory to explain
how it might have been possible. He
postulated that between 200 and 300
million years ago, all seven continents
were one giant landmass he called
Pangaea meaning “all lands." He also
suggested that Pangaea had split into
pieces and had, over time, drifted
(2) During Wagener’s
day, geologists believed
the continents were
once connected by land bridges and
were stationary. The idea that they
were once together, had somehow
drifted apart and were still moving,
sounded too far-fetched to be
believed.
(3) Wegener needed evidence to
support his theory. Just because it
looked like the continents fitted
together was not proof that they
© Continental Drift by Jim Cornish, 2007
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Figure 2: The earth as it was 300 million years ago (left) and as it is today (right). The arrows,
indicating motion, shows the continents are still moving- apart in some cases and colliding in
others.
Source: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter16/graphics/plate_tectonics.jpg
mountain ranges.
actually had. Then one day while
browsing in a library, he came across
a well-known list of plant and animal
fossils that were identical even though
they were found on opposite sides of
the south Atlantic Ocean. But it was
not enough to persuade supporters of
the land bridge connection to change
their minds.
(5) In Wegener’s day, most geologists
believed mountains formed when the
planet, once a molten ball, folded up
on itself as it shrunk while cooling.
Wegener thought his theory offered
better explanation. After studying the
Appalachian Mountains along the
eastern seaboard of North America
and the Scottish Highlands in Europe,
he discovered that the types and
layers of rock on both sides of the
Atlantic matched. That would only be
possible, Wegener argued, if North
America and Europe were once
(4) Despite the criticism directed at him
and his drifting continent theory,
Wegener did not give up. To him, the
idea made sense. All he needed was
more evidence and he found it when
he turned his attention to the earth’s
© Continental Drift by Jim Cornish, 2007
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were strong enough was discounted.
In 1929, Arthur Holmes, a geologist
and rare supporter of Wegener’s
theory, suggested that the earth’s thick
second layer, the mantle, had currents
powerful enough to carry the
continents sitting on top of them and
compared the process to a giant
conveyor belt. Holmes’ explanation
won Wegener many more supporters
but It would take thirty more years
before this explanation was taken
serious.
together and had later drifted apart.
(6) Wagener then went to the Arctic.
He found fossils of plants and animals
embedded in rocks millions of years
old. Since tropical organisms could not
possibly live in a frigid northern
climate, he reasoned that at one time
the Arctic landmasses must have been
located further south where, like today,
the climate is much warmer. Again, he
thought of drifting continents as an
explanation.
(9) By the 1960's, sciences such as
seismology (the study of earthquakes)
and volcanology (the study of
volcanoes) discovered much more
about the nature of the earth’s interior
than was known in Wegener’s time.
Some of the discoveries could only be
explained by continental drift and so
interest in the theory was rekindled.
(7) In 1915, Wegener published The
Origin of Continents and Oceans, a
book that outlined his theory and all
the evidence he had collected to
support his conclusions. Since his
ideas challenged long held beliefs
about the geological history of the
earth, he found very few supporters.
(8) Some of the criticisms directed at
Wegener were well founded. While his
evidence for drifting continents may
have been compelling, he had failed
to convincingly explain how it could
have happened. He explanation that
forces created by the earth’s rotation
(10) Today, a theory called plate
tectonics explains how continental drift
works. According to the theory, the
earth’s surface is fractured just like the
shell of a cracked egg. These fractures
© Continental Drift by Jim Cornish, 2007
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outline large
plate-like chunks
of the earth’
crust. Number
twelve in all they
include the
continents and/or
chunks of the
ocean floor. (See
Figure 3) These
plates
are
“floating” on the
mantle- drifting
apart 1-10 cm Figure 3: Plates of the earth’s surface and the location of active volcanoes.
Notice that the plate boundaries and most active volcanoes occur very near
yearly in some each other.
areas
and
2006, after ten years of measuring,
colliding in others. Earthquakes and
these satellites proved what Wegener
volcanoes occur more often along the
believed all along- Europe and North
edges of these plates than anywhere
America are moving apart and about
else on earth. Mountain ranges such
1.5 centimetres per year.
as the Rockies of North America, the
Himalayas of Asia and the Alps of
(12) Although still called a theory and
Europe are forming where the
still being supported by new evidence
continents are colliding.
each year, continental drift has been
accepted by virtually all geologists as
(11) Proof of drifting continents is
scientific fact.
coming from special satellites orbiting
the earth. Using global positioning
technology even minute shifts in the
earth’s surface can be detected. In
© Continental Drift by Jim Cornish, 2007
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On the Move:
Continental Drift and Plate Tectonic
By Jim Cornish
1. Vocabulary:
Match the definitions below with a word from the paragraph indicated in
parenthesis.
a.
(1)
supposed, assumed . . . . . . . . . . . . . . . . . . . . . . . . _________________________
b.
(2)
still, not moving . . . . . . . . . . . . . . . . . . . . . . . . . . _________________________
c.
(3)
an unproven idea . . . . . . . . . . . . . . . . . . . . . . . . . . _________________________
d.
(4)
something that supports a theory . . . . . . . . . . . . . _________________________
e.
(5)
scientists who study rocks and earth’s history . . . _________________________
f.
(6)
a part of, inside . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________________
g
(7)
solution to a problem . . . . . . . . . . . . . . . . . . . . . . _________________________
h.
(8)
comments, usually bad ones . . . . . . . . . . . . . . . . . _________________________
i.
(9)
renewed, revived . . . . . . . . . . . . . . . . . . . . . . . . . . _________________________
j.
(10)
split into pieces . . . . . . . . . . . . . . . . . . . . . . . . . . . _________________________
2.
Using the information from paragraph eight, write a definition for each of the following.
Seismologist ____________________________________________________________
vulcanologist ____________________________________________________________
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Reading Comprehension
1.
What evidence did Wegener present to support his theory of continental drift?
2.
What was the early reaction to Wegener’s theory?
3.
How is the earth’s surface similar to a cracked egg?
4.
What modern technology is providing proof to support the theory of continental drift?
Inferential
1.
Why do you think the reaction to Wegener’s theory gradually changed in favour of his
theory?
Opinion
1.
What do you think of the theory of continental drift?
By the Numbers
Provide a numerical answer for each of the following.
a.
the distance North America and Europe move apart yearly . . . . . ___________________
b.
the year Wegener first developed his drifting continent theory . . ___________________
c.
the time long ago when the continents were one landmass . . . . . ___________________
d.
the year Wegener published his book on drifting continents . . . . ___________________
e.
the year interest in Wegener’s theory increased . . . . . . . . . . . . . . ___________________
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Visual Literacy
1.
What can you say about the location of active volcanoes and boundaries of the tectonic
plates of the earth?
2.
How do you think the ring of fire got its name?
3.
How have most of the tectonic plates been named?
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