The collision began in the Upper Cretaceous period about 70 million years ago, when the north-moving Indo-Australian Plate, moving at about 15 cm (6 in) per year, collided with the Eurasian Plate. About 50 million years ago, this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor, and the volcanoes that fringed its edges. Since these sediments were light, they crumpled into mountain ranges rather than sinking to the floor. The Indo-Australian plate continues to be driven horizontally below the Tibetan plateau, which forces the plateau to move upwards; the plateau is still rising at a rate of approximately 5 mm (0.2 in) per year.
Animal and plant life[edit]
Pastoral nomads camping near Namtso.
Tibet's elevation and lack of precipitation produces an alpine tundra environment, which reduces species diversity. Tibet hosts species of wolf, snow leopard, wild yak, wild donkey, cranes, vultures, hawks, geese, snakes, and buffalo. One notable animal is the high-altitude jumping spider, that can live at elevations of over 6,500 metres (21,300 ft).[17]
Nomadic culture[edit]
Nomads on the Tibetan Plateau and in the Himalayas are the remainders of nomadic practices historically once widespread in Asia and Africa.[18] Pastoral nomads constitute about 40% of the ethnic Tibetan population.[19] The presence of nomadic peoples on the plateau is predicated on their adaptation to survival on the world's grassland by raising livestock rather than crops, which are unsuitable to the terrain. Archaeological evidence suggests that the colonization leading to the full-time occupation of the plateau occurred much later than the previously thought 30,000 years ago
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