The province of Alberta, Canada, has a history and prehistory stretching back thousands of years. The ancestors of today's First Nations in Alberta arrived in the area by at least 10,000 BC, according to the Bering land bridge theory. Southerly tribes, the Plain Indians, such as the Blackfoot, Blood, and Peigans eventually adapted to seminomadic plains bison hunting, originally without the aid of horses, but later with horses that Europeans had introduced. Recorded or written history begins with the arrival of Europeans. The rich soil was ideal for growing wheat and the vast prairie grasslands were great for raising cattle. The coming of the railways in the late 19th century led a to large-scale migration of farmers and cattleman from Eastern Canada, the United States, and Europe. Wheat and cattle remain important, but the farms are much larger now and the rural population much smaller. Alberta has urbanized and its economic base has expanded from the export of wheat and cattle to include the export of petroleum as well. Native groups More northerly tribes, like the Woodland Cree and the Chipewyan also hunted, trapped, and fished for other types of game in the aspen parkland and boreal forest regions. Later, the mixture of these native peoples with French fur traders created a new cultural group, the Métis. The Métis established themselves to the east of Alberta, but after being displaced by white settlement, many migrated to Alberta. Political history of the indigenous peoples Following the arrival of outside European observers it is possible to reconstruct a rough narrative history of the nations of what later became Alberta. Using later-recorded oral histories as well as archaeological and linguistic evidence, it also possible to make inferences back further in time. In both cases the evidentiary base is thin, however. It is believed that at least some parts of the Great Plains were depopulated by a prolonged period of the drought during the Medieval Warm Period (). The area was repopulated once the drought subsided, by peoples from a diverse number of language families and from all parts of the North American continent. The Numic languages (for example Comanche and Shoshoni) are from the Uto-Aztecan language family and came to the Plains from the southwest. Algonquian speakers (Plains Cree, Blackfoot, Saulteaux) are originally from the northeast. The Siouxan peoples (Great Sioux, Assiniboine, Nakoda, Mandan, Crow, etc.) speak a family of languages different from