© 1995-2001 Untangle Incorporated
Last Updated: Wednesday,December 1, 1999
Plate Tectonics: A Brief Explanation
The continents of mainly granite rock arise out of basalt rock three kilometers below them. The balsalt beneath the continent extends outside the continent and if the whole structure could be seen from above it would be like a plate. The plates, about 3 to 6 kilometers thick float on a molten rock closer to the center of the earth. The rock ia molten as it is continuously heated by radioactive elements decaying inside the earth. As there is more than one place where the decay is occuring the currents of molten rock is not all in one direction but is pushing (at the edges of any one particular flow) against the other flow. A continent above this flow is pushed in the general direction of the flow, but other continents are moving in different directions so collisions are inevitable.
These moving continental plates bump into each other then. If these plates all had the same strength, the same shape at the same depth below the surface it would just be continental bumper cars. However because none of those things are the same in each plate then when one plate strikes another, plates crack and/or move the edge of one slightly higher, or lower at the point of contact. This is the process which leads to mountains, and rifts and earthquakes, and where most of the volcanic activity arises.
As an example take the day the African continental plate met the Asian continental plate.
The African continental plate moved in a north east direction into the Asian continental plate. As the African plate was at that spot slightly lower and overall is lighter than the Asian plate, the African plate started to slip down there in the east beneath the Asian plate. The land behind this falling plate rose. Fossils of the plants and animals of that period in that north east area show that it was heavily forested, a jungle, all the way west to the Atlantic and all the way north to the European penisula.(Note 1)
The land that was moving up moved up into the air some 3,000 meters in 3,000,000 years. That upward motion of the land totally changed the weather pattern west and east of it (since the air moving west to east, with rain, now had to go up, and as air goes up it cools. Cooler air can hold less water vapor, so there is rain on the West side of the uplift, and less rain falls on top of the uplift, and east of it.
This collision started about 15,000,000 million years ago, and the uplift by 3,000 was over by 12,000,000 millions years ago.
References:
Introduction
Plate Tectonics
Dynamic Earth
NOTES:
1.The Mediterranean sea did not exist then. The Atlantic would not break through where Gibralter is today for another 10 million years.
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