Plate Tectonics is a scientific theory by which the origin
of most of the major features seen on the Earth’s surface are explained. This
theory tells us that the Earth has an outer shell made up of 30 rigid pieces,
called tectonic plates, some of which are vast: most of the Pacific region
covers a single plate. The movement of the plates is responsible for the
faulting and folding of the earth’s crust, creating volcanoes, mountain ranges
and so on. The plates are able to move on the layer of molten rock beneath,
which is so hot that it flows though it remains solid. The plates move up to
10 cm a year.
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| Tectonic Plates |
What are Continental Shelves?
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| Continental Shelf |
The continental margin forms the part of the sea bed that
borders the continent. It consists of the continental shelf, the continental
slope and the continental rise. The continental shelf is the submerged land at
the edge of the continents. It begins at the shoreline and gently slopes
underwater to an average depth of about 130 metres. The width of the continental
shelf averages 75 km. In certain areas, such as parts of the Arctic region, the
shelf extends as far as 1600 km. In some other areas, particularly those
bordering much of the Pacific, it measures only 1.6 km or less. Valleys of varying
depths cut through the shelf.
What did the continents look like before?
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| Pangea |
When the Earth formed, the lighter elements floated to the
surface, where they cooled to form a crust. The first rocks were formed over
3500 years ago, but they have not remained static. The coastlines on the either
side of the Atlantic appear to fit together like a jigsaw, and thought that all
the masses were once joined together, forming a super continent called Pangea.
Changed by forces, outside and inside the Earth, Pangea divided to form the
continents we know today.
What shape are the sea floors?
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| Sea floor spreading |
The bottom of the ocean has features as varied as those on
land. Huge plains spread out across the ocean floor, and long mountain chains
rise toward the surface. Volcanoes erupt from the ocean bottom, and deep
valleys cut through the floor. In the early 1960’s, a theory called Sea-Floor
spreading provided some explanation. According to the theory the sea floor itself moves carrying the continents along. Circulating movements deep
within the Earth’s mantle make the sea floor move. The circulating movements
carry melted rock up the mid-ocean ridges and force it into the central valleys
of the ridges. As the melted rock cools and hardens, it forms new sea floor and
pushes the old floor and the continents away from the ridges.
Fact Files
- Movement of the land is still taking place as India and Asia are colliding, forming the Himalayas. This movement is called continental drift.
- Plates have been moving about for hundreds of millions of years. So, in spite of their very slow speeds some of them have covered vast distances over the past several years.
- A hot vent is a chimney like structure on the ocean floor,that discharges hot, mineral rich water. Scientists have observed hot vents in 1977.
- The continental rise consists of sediment from the continental shelf that accumulates at the bottom of the slope. These deposits can extend up to can extend up to about 1000km from the slope.
