Chapter 33
Our Restless Planet
The theory of continental drift
Until recently it was thought that the crust of the Earth was solid and
stable in position. It was obvious that there were wrinkles in the crust in the
form of mountain ranges and some movement in the form of earthquakes,
but it was thought that these phenomena were the result of contraction of the
crust as the Earth slowly cooled and solidified.
Many people had observed, however, the strange coincidence in the
shapes of the coastlines of the eastern and western sides of the Atlantic
Ocean. In the early 20th century Alfred Wegener studied this situation. He
found that the above water land masses of South America and Africa seemed
to fit like pieces of a jigsaw puzzle, and that the continental shelves fit even
more closely. He found that fossils of ancient plants and animals seemed to
match up both sides of the Atlantic. This evidence led him to propose that
the continents of Africa, Europe, North America and South America were,
millions of years ago, part of one larger land mass called Pangaea which has
since split up. Such an arrangement would explain the strange glacial
evidence found at various places on the present continents. If the continents
were where they are today, glaciers must have crossed the equator. If the
continents have moved the glaciers could all have been confined to much
higher latitudes.
In 1915 Wegener published his hypothesis, which came to be called
continental drift. Although Wegener showed much evidence to back up his
idea that the continents had moved, he could not provide an adequate
explanation of how they moved. This situation was similar to the status of
evolution before Charles Darwin. Other scientists has recognized that life
forms had changed drastically over great periods of time, but it was Darwin
who provided the first explanation of how life changes through the process
of natural selection.
Without a mechanism to explain continental drift most scientists
dismissed the idea. It was not until the 1950’s that new evidence brought
renewed interest in continental drift.
