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RUNING HEAD: THE CONTINENTAL DRIFT THEORY
The Continental Drift Theory
Benjamin Bogan
SCI101-1303B-11: Introduction to the Sciences
9/16/13
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THE CONTINENTAL DRIFT THEORY
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The Continental Drift Theory
The continental drift theory was developed by a German scientist, Alfred Wegener. In his
book, The Origin of Continents and Oceans, he argued that the continental landmasses were
drifting across the earth. He based this on the fact that the coast of Western Africa and South
America looked like the edges of interlocking pieces of a jigsaw puzzle. He was thus convinced
that the two were once part of an enormous single landmass known as Pangaea before it split
apart. This was supported by geological and biological similarities in these areas. The
development of this theory spearheaded a lot of research since many scientists did not agree with
the idea. It led to more developments in the mid and late 20th century that proved that the
landmasses were in constant motion. The additions on the Wegener’s evidence include
paleomagnetism and seafloor spreading.
Paleomagnetism is the study of the intensity and orientation of the Earth’s magnetic field
as preserved in the magnetic orientation of certain minerals present in rocks. Many scientists
have explored this field to find evidence of continental drift. When hot magma rises and cools
on the surface of the Earth, the minerals present become magnetized in alignment with the
Earth’s magnetic field. Rocks formed at different places on the Earth’s surface have different
magnetizations. Some rocks have magnetizations that do not agree with their position on the
Earth but this is due to the wandering of the Earth’s magnetic poles. Using the alignment of
magnetic minerals in the rock layers, the movement of the magnetic poles could be traced
through the different geologic periods. The record of direction and intensity of magnetic field
kept by certain minerals in rocks provide information on the past behavior of Earth’s magnetic
field and the past location of tectonic plates. This is therefore an evidence of landmasses drifting.
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The magnetized minerals also show the direction to the Earth’s magnetic poles and provide a
means of determining their latitude of origin. Polar wandering, which is the apparent movement
of the magnetic poles illustrated in rocks, indicates that continents have moved. This is shown in
polar wandering curves. The curves for North America and Europe have similar shapes but are
separated by about 240 of longitude. The difference between the paths can be reconciled if the
continents are placed next to one another.
In 1962, Harry Hess, a geologist and an army commander during the World War II,
added a geologic mechanism to account for Wegener’s moving continents. During his work to
determine the deepest part of the sea, he discovered hundreds of flat-topped mountains that
shaped the floor of the Pacific Ocean. He thus proposed the sea floor spreading as an evidence of
continental drift. He proved Wegener’s idea right and clarified the mechanism that broke the
once joined continents. Sea floor spreading is the process in which the ocean floor is extended
when two plates move apart forming cracks. Magma rises through the cracks and seeps out onto
the ocean floor like a long thin undersea volcano. The sea floor moves in a conveyor belt fashion
thus explaining the phenomenon of the youngest rocks being found only at the mid ocean ridges
and they get older as they move away from the ridge. Mantle convection at plate boundaries of
the sea floor is the driving force for the motion of the floor and the continents themselves. When
hot magma rises, it cools and hardens upon reaching the surface. As more magma rises the
present sea floor is pushed aside making the cold and dense rocks to sink and melt becoming
magma again. Sea floor spreading was developed due to the understanding of the plate tectonic
theory. At this zone where two oceanic plates are moving away from each other, there
is the formation of new crust. This is known as a constructive zone. Features such as the Mid
Atlantic Ridge were formed due to this thus clear evidence that continents are drifting.
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The Wegener’s hypothesis of continental drift was earlier rejected by scientists because it
lacked a mechanism which would have led the continents to drift. He did not explain clearly how
the continents moved which would have made it easy to justify the time it took for the present
day continents to move to where they are. During that time it was also hard to accept that the
continents are in constant motion since no major evident motion had been witnessed. His ideas
were however accepted in the mid-20th century with the development of other geological
evidence to supplement his earlier findings. The plate tectonic theory illustrated clearly,
explaining that the Earth’s crust is made up of plates which are in constant motion thus the
drifting of continents. Other evidence such as the sea floor spreading also made scientist to agree
to Wegener’s hypothesis. The other reason that may have led to rejection of Wegener’s idea may
be because it had not gone through the scientific method of theory development thus it could not
be accepted without enough testing for approval. Scientists today accept the movement of
continents since the hypothesis was tested and became a theory.
The scientific method is the act of scientists, collectively over time, creating models of
the natural world that can be verified experimentally. The method involves observation, data
collection and recording and analyzing in a form that can be duplicated by other scientists. The
method involves four important steps i.e. observation and description of phenomena, hypothesis
formulation to explain the phenomena, testing the hypothesis by analyzing the results of
observation or by predicting and observing the existence of new phenomena that follow from the
hypothesis, and establishing a theory based on repeated verification of the results. The
hypothesis is only regarded as a theory or law of nature if the experiments bear out. If the
experiments do not bear out, the hypothesis must be rejected or modified. This method is helpful
THE CONTINENTAL DRIFT THEORY
in the understanding of the natural world since it is empirical. It minimizes the influence of
personal and cultural beliefs when developing a theory.
The Wegener’s hypothesis of movement of continents was rejected by scientists because
it did not have a mechanism which initiated the movement. They later accepted with the
development of plate tectonic theory which provided a mechanism for continental drift. The
Earth’s crust is made of plates which move away from each other, towards each other and slide
past one another. The plates include both oceanic and continental namely; Eurasian, AustralianIndian, Philippine, Pacific, Juan de Fuca, Nazca, Cocos, North American, Caribbean, South
American, African, Arabian and the Antarctic plate. These movements initiate the movement of
continents due to the forces involved. At the constructive zone for example, the mantle
convection is a driving force for the motion of the sea floor and the continents. The forces of
extension in this boundary also lead to plate movement in opposite directions thus movement of
continents. Since most plates include an entire continent plus a large area of the sea floor, when
the plates move, the continents move.
When two continental plates move away from each other, a rift valley is formed. This is
accompanied by volcanic activities on the floor thus formation of volcanic features. In the case
of oceanic plates, mid oceanic ridges are formed. When an oceanic plate collides with a
continental plate, the oceanic is forced underneath the continental plate, a process known as
subduction. This zone is characterized by volcanic and seismic activities due to the energy
generated. An example is the Pacific ring of fire. When two continental plates collide, fold
mountains such as the Himalayas are formed.
The continental drift has today gained the support of scientists due to evidence such as
plate tectonics which were developed to support the Wegener’s argument.
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References
Edwards, J. (2005). Plate tectonics and continental drift. London, United Kingdom: Evans
Brothers.
Frisch, W., Meschede, M., & Blakey, R. C. (2010). Plate tectonics: Continental drift and
mountain building. New York, NY: Springer.