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Geology of Himalayas

Ranges And Origin

The Himalayas are also made up of four distinct ranges. The northernmost Trans-Himalayas, the Greater or Tibetan Himalayas, the Lesser or Lower Himalayas, and the southernmost Outer Himalayas parallel each other in long belts from west to east. Each has a different geologic history depending on how, where, and when (in geologic time) the tremendous plates that make up Earth's crust collided and pushed up the ranges. Plate tectonics is a geologic theory that describes the crust of the Earth as a collection of plates floating on the molten mantle; scientists believe the movement (tectonics) is the planet's effort to keep itself cool.

Before the Jurassic Period (180 million years ago), India, South America, Africa, Australia, and Antarctica were united as one giant, southern "super continent" called Gondwanaland or Gondwana. In Jurassic times, this super continent began to break into fragments that moved away from each other. India began to move northward toward Eurasia, but, between the Eurasian Plate and the Indian Plate, was the Tethys Trench which was a deep ocean. The Indian Plate moved to the north over the course of 130 million years; in the Tertiary Period (50 million years ago), it finally collided with Eurasia. Collisions like this between continents typically take millions of years and involve volcanism, seismic activity, metamorphism (changes) of rocks due to intense pressure, and episodes of mountain-building. Scientists have been able to use the metamorphic rocks in the Himalayas to date these events by measuring radioactivity remaining in the rocks.

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Science EncyclopediaScience & Philosophy: Heterodyne to Hydrazoic acidGeology of Himalayas - Ranges And Origin, Mountain Building, Seismic Activity