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The Natural Environment

Geological History

According to the theory of plate tectonics, the crust of the Earth’s surface is made up of vast continental and oceanic plates. These are in constant motion, rubbing and pushing against one another, moving only small amounts each year. The Eurasian continental plate is the largest. It is composed of some of the most ancient rocks on Earth, originating in Precambrian time from 4.65 billion to 570 million years ago. These ancient materials can today be found in eastern Siberia, throughout the Arabian Peninsula, and in India south of the Indus and Ganges rivers.

A huge sea called Tethys covered most of the interior of Eurasia during the Paleozoic and Mesozoic eras, which lasted from 570 million to 65 million years ago. Thick deposits of sediment formed on the seafloor, eventually becoming the layers of rock that form the geological features of the present day.

The Indian subcontinent broke off from the southeastern corner of the African continental plate during the Cretaceous period. It drifted in a northeasterly direction and collided with the larger Eurasian plate, slipping partly underneath it. The impact created an enormous “deep” that eventually filled with sediments and became the Gangetic Plain. The collision also generated enormous pressure on the southern edge of the Eurasian plate, causing this region to crumple; this forced an uplift of rock that created the Himalayas, the world’s highest mountain system.

The Pacific Ocean plate drifted westward, scraping along the Eurasian plate and slipping under its coastal edge. This created the islands of Japan, Taiwan, the Kurils, the Ryukyus, and the Philippines. Southeast Asia lies at the intersection of the Eurasian, Pacific Ocean, and Indian Ocean plates. Over time the contact between these plates created the mountain ranges of mainland Southeast Asia. The continued slow movement of the plates causes friction and instability deep below the Earth’s surface, producing volcanoes and earthquakes.

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