NCERT Book Class 11 Geography (Fundamental of Physical Geography) Chapter 4 Distribution of Oceans and Continents

CHAPTER

DISTRIBUTION OF OCEANS
AND CONTINENTS

In the previous chapter, you have studied the theory” in 1912. This was regarding the
interior of the earth. You are already familiar distribution of the oceans and the continents.
with the world map. You know that continents According to Wegener, all the continents
cover 29 per cent of the surface of the earth formed a single continental mass and mega
and the remainder is under oceanic waters. ocean surrounded the same. The super
The positions of the continents and the ocean continent was named PANGAEA, which meant
bodies, as we see them in the map, have not all earth. The mega-ocean was called
been the same in the past. Moreover, it is now PANTHALASSA, meaning all water. He argued
a well-accepted fact that oceans and that, around 200 million years ago, the super
continents will not continue to enjoy their continent, Pangaea, began to split. Pangaea first
present positions in times to come. If this is broke into two large continental masses as
so, the question arises what were their positions Laurasia and Gondwanaland forming the
in the past? Why and how do they change their northern and southern components
positions? Even if it is true that the continents respectively. Subsequently, Laurasia and
and oceans have changed and are changing Gondwanaland continued to break into various
their positions, you may wonder as to how smaller continents that exist today. A variety of
scientists know this. How have they determined evidence was offered in support of the
their earlier positions? You will find the answers continental drift. Some of these are given below.
to some of these and related questions in this
chapter. Evidence in Support of the Continental Drift
CONTINENTAL DRIFT The Matching of Continents (Jig-Saw-Fit)
Observe the shape of the coastline of the Atlantic The shorelines of Africa and South America
Ocean. You will be surprised by the symmetry facing each other have a remarkable and
of the coastlines on either side of the ocean. No
unmistakable match. It may be noted that a
wonder, many scientists thought of this
map produced using a computer programme
similarity and considered the possibility of the
to find the best fit of the Atlantic margin was
two Americas, Europe and Africa, to be once
presented by Bullard in 1964. It proved to be
joined together. From the known records of the
quite perfect. The match was tried at 1,000-
history of science, it was Abraham Ortelius, a
fathom line instead of the present shoreline.
Dutch map maker, who first proposed such a
possibility as early as 1596. Antonio Pellegrini
Rocks of Same Age Across the Oceans
drew a map showing the three continents together.
However, it was Alfred Wegener—a German The radiometric dating methods developed in
meteorologist who put forth a comprehensive the recent period have facilitated correlating the
argument in the form of “the continental drift rock formation from different continents across