GREENLAND: Beginning in A.D. 985, Norse Vikings established a string of settlements in Greenland that thrived for around 400 years. Supported by animal husbandry, the population peaked at around 2,000 before people abruptly abandoned the island in the early 15th century. Experts had believed that a rapid drop in temperature drove the settlers out, but recent sediment analysis from a lakebed near one of their farmsteads indicated that the temperature actually remained steady. Instead, conditions suddenly became much drier, curtailing the growth of grass, which was vital for the survival of livestock.