THE UNIQUE EARTH AND GEOMORPHOLOGY
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| Land Ahoy |
| Meanwhile there was constant flow of heat from the
very hot interior to the exterior. This was not conducted away to
the outside, as the lithosphere was a poor conductor. Hence the excess
energy found outlet through vents of volcanism. This gradually built
mid oceanic ridges and in the southern hemisphere some of the lithosphere
rose above the water, creating the first islands or an archipelago.
Still there was no continent or a landmass of any considerable size.
For more than three billion years our planet remained a huge ocean,
with some islands and frozen water around the pole. The first super
continent was formed some 700 million years ago, most of the land
being in the southern hemisphere. Geologists call this landmass Pangaea. |
| A Jigsaw Puzzle |
| We have got used to the idea that the earth is rotating
on its axis rather fast and flying round the sun every year. And now
comes this notion that the surface of the earth is not at rest at
all. The continents are always moving ever so slightly, some very
slow, others comparatively fast. The branch of geomorphology called
plate tectonics dealing with the movements of continental plates and
ocean plates was born in the fifties. About 200 million years ago
the single continent of Pangaea started breaking up. 180 million years
ago there were two landmasses the northern one called Laurasia and
the southern one Gondwanaland. These two were still nominally joined
at Gibraltar. Then Gondwanaland began breaking up. About 130 million
years ago, Africa, retaining South America, Arabia and Madagascar
began moving north, away from the southern most landmass comprising
of Antarctica and Australia as a single piece. Later the Indian plate
also had broken up from Africa and began moving north. The present
island of Madagascar was joined with the Indian plate. |
| 65 million years ago South America broke off from Africa.
The Madagascar separated from the Indian plate. The Indian plate reached
the equator in its flight to join Asia. Africa disengaged from Europe
at Gibraltar but a new link to Asia was made at Suez, though Arabia
was still part of the African landmass. Australia was still joined
to Antarctica though the Australian section had moved further north.
While all these changes were happening in the southern hemisphere,
the northern part, Laurasia seemed to have undergone very little change.
Though this part began breaking up, the Canadian section was still
fully joined to the western European section. The various pieces of
the Jig saw puzzle on the earth’s crust was placed in their
present positions during the last 50 million years. There were some
very remarkable events in this relatively short span of time in earth’s
history. |
| During this period: |
| 1) |
North America broke off from Europe and joined up with
South America. |
| 2) |
Australia broke off from Antarctica and moved further north |
| 3) |
The fault line that created east African rift valley system also
created the red sea separating Arabia from Africa except for the Suez
connection. |
| 4) |
This period also saw the birth of many of the present islands including
all the islands of the South-East Asia, the British Isles and Sri
Lanka. One of the youngest islands is the Hawaii. |
| 5) |
The Indian plate moving up north joined up with the Asian landmass |
| Of all these the most dramatic event was the fusion
of the Indian plate with the Asian continental mass. The force of
this collision gave birth to the rise of the greatest mountain range
in the world, the Himalayas. It was also this event that gave rise
to a new climatic phenomenon, the monsoons. According to some geologists,
the Indian plate is still moving northwards at a rate of something
like 2 cm per year. Is this going to push the Himalayas and Everest
still higher than it is now. Not likely. They suggest that the Indian
plate is sliding under the continental mass and the result could be
catastrophic earthquakes that could affect many densely populated
areas from Kashmir to the Ganges delta. |
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