A from one super�continent, called
Pangaea. The super-continent,
by mid-Jurassic, 150 million years ago,
Pangaea had split into a northern continent
called Laurasia, and a southern continent
called Gondwanaland. About 65 million years ago, i.e. at the end of Cretaceous,
Gondwanaland further broke up to give rise to
several other continents such as South
America, Africa, Australia, and Antarctica.
India broke apart and followed an
independent route moving towards northeast.
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EVIDENCE OF MOVEMENT OF CONTINENTS
There are evidences that suggest the
existence of Pangaea. The ancient mountain
belt, 470 to 350 million years old, were created
by a continuous belt of geological activity.
These mountains are now separated by the
Atlantic Ocean. Some fossils also tell us that
the continents were once joined. For example,
fossils of the plant Glossopteris and the
animals Mesosurus and Lystrosaurus have all
been found on all continents of Gondwanaland
that are now widely separated.
Geological Matching
Significant observation is the occurrence of
gold deposits within river alluvium in the
Ghana coast (Africa) and the absolute absence
of source rocks in that region. However, across
5,000 km wide ocean, there are gold-bearing
veins in Belen Sau in Brazil (South America)
but no gold deposits within alluvium in the
adjacent coastal belt. Placing Africa and South
America together, the solution emerges with
stunning effectiveness. The gold bearing
sediments were transported down the slope in Brazil
and deposited in the belt which is today the Ghana coast.
Palaeoclimatic Unity
Thick glacial deposits of Permo-Carboniferous
age are exposed at Uruguay and Brazil in
South America, Africa, south India, south
Australia and Tasmania. The uniformity in the
nature of sediment indicates that these
continents/countries were together in the
geological past and experienced similar
climatic conditions. Today, these countries are
situated in various types of climatic zones,
from temperate to tropical and are widely
separated from each other by large oceans.
Similarly, corals thrive in warm waters
between the latitudes 300N and 300S. However,
remnants of some corals found on the continents
away from the region strengthen the view that
these continents were nearer to the equator in
the geological past. The continents have moved
northwards and are experiencing cold and frigid
climatic conditions today.
Polar Wandering
One of the strongest line of evidence that the
continents were formerly united in Pangaea
came from palaeomagnetism. The magneti-cally
susceptible minerals such as magnetite,
haematite, ilmenite, pyrrhotite in lava/magma
and unconsolidated sediments have the
tendency to align themselves parallel to the
magnetic field prevailing at that time. This
property is retained in the rocks as permanent
magnetism. There has been periodic change in
the position of magnetic pole that is recorded
in rocks by way of permanent magnetism.
Unraveling the signatures of such changes in
the geologically old rocks by scientific methods
provides the changing position of poles in
geological time scale. This is known as polar
wandering. The polar wandering clearly
demonstrates that the continents have
frequently moved and changed directions of
their motion from time to time.