There is no evidence as yet that early hominids settled in Mongolia, most likely because of the inhospitable terrain and climate. Most of Mongolia is high above sea level; much of the western, northern, and central part is mountainous; the rest is taken up by the Gobi Desert. It is a dry climate, with extremely cold, windy winters; parts of Mongolia experience hot summers. About 200,000 B.C., perhaps earlier, some archaeological evidence indicates human (probably archaic Homo sapiens) presence in the Gobi Desert in southern Mongolia. Thereafter the evidence of human settlement in Mongolia is scant, but clearly Homo sapiens have moved into this region; there are many finds of stone tools dating from 50,000 B.C. on. Eventually these people establish the nomadic way of life that will prevail even to the end of the twentieth century: it is based on following herds of various animals such as sheep, goats, and yaks while living in their portable felt tents (ger). Probably during the second millennium B.C. these early Mongolians are among the first to domesticate horses for their own uses; later they also adopt the camel. Not until the third century B.C. do Chinese sources begin to refer to a consistently identifiable culture in the region of the Mongolian steppes. For the next fourteen centuries, various groups of people rise and fall in power in the region that today comprises Mongolia and the bordering provinces of northern China (including the vast region now called Inner Mongolia). Some of these peoples are from Mongolia and neighboring Manchuria, some are Turks from the west. In the early seventh century A.D. Chinese of the Tang dynasty commence a series of campaigns and by 744 have driven out the Turks, but then another Turkic people, the Uyghurs, become the dominant force in this region. The Uyghurs' power collapses about 840 and a period of relative anarchy ensues, with tribesmen from Manchuria, first the Khitan and then the Jurchen, becoming the main power. It is not until about 1125 that the people who will become known in history as the Mongols begin to emerge as the major force in this region.