Continental Drift
‘‘Continental drift’’ is the movement of the Earth’s continents in relationship to
each other. When looking at the Earth’s globe one is tempted to fit the South
American continent with the West coast of Africa, and when looking closer
towards the northern hemisphere, Europe and North America could also fit together with a small rotation with respect to each other.
The first hint of a theory for the drift of the continents was mentioned in 1620
by Francis Bacon, who suggested that the western hemisphere was once attached
to Europe and Africa. However, the idea that the continents were once joined
together was first put forward by the Flemish cartographer, Abraham Ortelius, in
1596. These ideas were more fully developed by the German astronomer, Alfred
Wegener, in 1912. He proposed that all the continents were attached together 200
million years ago and he called this super-continent ‘‘Pangaea’’ (Fig. 2.6).
Wegener also used paleontological records, which reported that fossils of some
animal species found on both the American and African continents had similarities. It was also in the nineteenth century that Eduard Suess, a geologist from
Austria, noted a close correspondence between certain geological formations on
the southern hemisphere continents of Australia, Antarctica, southeast Asia and
India. Based on his observations, Suess suggested that these areas were once part
of an original, large landmass he named Gondwana.
Scientists did not accept Wegener’s concept of continental drift until after his
death, which occurred during an expedition to Greenland, in 1930. In fact, many
scientists were not convinced about the drift of continents even up to the 1960’s.
However, the final irrefutable verification that the continents have been drifting
apart came in 1963 when two British scientists, Vine and Matthews, reported the
result of their investigations on the magnetic imprint left by the Earth’s magnetic
field at spreading ridge axes (See Chap. 7). It was at this point that the theory of
Continental Drift was finally accepted.
Plate Tectonics
The ‘‘theory of plate tectonics’’, which involves the movement of the rigid
segments (plates) of the Earth’s lithosphere, was inspired by and evolved from
Wegener’s earlier hypothesis concerning continental drift. This theory has considerably changed our perception about how we view our living planet. The Plate
Tectonic Theory was first presented in 1967 at the American Geophysical Union
(AGU) meeting in Washington DC by Jason Morgan. According to his explanation, the surface of our planet is divided into several rigid plates that are moving
with respect to each other. These rigid plates, which include the Crust and the
Lithosphere, move above a less rigid substratum called the asthenosphere
(Fig. 2.3). Jason Morgan and Xavier Le Pichon wrote and published the first
Continental Drift
41
‘‘Continental drift’’ is the movement of the Earth’s continents in relationship to
each other. When looking at the Earth’s globe one is tempted to fit the South
American continent with the West coast of Africa, and when looking closer
towards the northern hemisphere, Europe and North America could also fit together with a small rotation with respect to each other.
The first hint of a theory for the drift of the continents was mentioned in 1620
by Francis Bacon, who suggested that the western hemisphere was once attached
to Europe and Africa. However, the idea that the continents were once joined
together was first put forward by the Flemish cartographer, Abraham Ortelius, in
1596. These ideas were more fully developed by the German astronomer, Alfred
Wegener, in 1912. He proposed that all the continents were attached together 200
million years ago and he called this super-continent ‘‘Pangaea’’ (Fig. 2.6).
Wegener also used paleontological records, which reported that fossils of some
animal species found on both the American and African continents had similarities. It was also in the nineteenth century that Eduard Suess, a geologist from
Austria, noted a close correspondence between certain geological formations on
the southern hemisphere continents of Australia, Antarctica, southeast Asia and
India. Based on his observations, Suess suggested that these areas were once part
of an original, large landmass he named Gondwana.
Scientists did not accept Wegener’s concept of continental drift until after his
death, which occurred during an expedition to Greenland, in 1930. In fact, many
scientists were not convinced about the drift of continents even up to the 1960’s.
However, the final irrefutable verification that the continents have been drifting
apart came in 1963 when two British scientists, Vine and Matthews, reported the
result of their investigations on the magnetic imprint left by the Earth’s magnetic
field at spreading ridge axes (See Chap. 7). It was at this point that the theory of
Continental Drift was finally accepted.
Plate Tectonics
The ‘‘theory of plate tectonics’’, which involves the movement of the rigid
segments (plates) of the Earth’s lithosphere, was inspired by and evolved from
Wegener’s earlier hypothesis concerning continental drift. This theory has considerably changed our perception about how we view our living planet. The Plate
Tectonic Theory was first presented in 1967 at the American Geophysical Union
(AGU) meeting in Washington DC by Jason Morgan. According to his explanation, the surface of our planet is divided into several rigid plates that are moving
with respect to each other. These rigid plates, which include the Crust and the
Lithosphere, move above a less rigid substratum called the asthenosphere
(Fig. 2.3). Jason Morgan and Xavier Le Pichon wrote and published the first
Continental Drift
41