Environmental history is the study of human interaction with the natural world over time, emphasising the active role nature plays in influencing human affairs and vice versa. Environmental history first emerged in the United States out of the environmental movement of the 1960s and 1970s, and much of its impetus still stems from present-day global environmental concerns. The field was founded on conservation issues but has broadened in scope to include more general social and scientific history and may deal with cities, population or sustainable development. As all history occurs in the natural world, environmental history tends to focus on particular time-scales, geographic regions, or key themes. It is also a strongly multidisciplinary subject that draws widely on both the humanities and natural science. The subject matter of environmental history can be divided into three main components. The first, nature itself and its change over time, includes the physical impact of humans on the Earth's land, water, atmosphere and biosphere. The second category, how humans use nature, includes the environmental consequences of increasing population, more effective technology and changing patterns of production and consumption. Other key themes are the transition from nomadic hunter-gatherer communities to settled agriculture in the neolithic revolution, the effects of colonial expansion and settlements, and the environmental and human consequences of the industrial and technological revolutions. Finally, environmental historians study how people think about nature - the way attitudes, beliefs and values influence interaction with nature, especially in the form of myths, religion and science. Origin of name and early works In 1967, Roderick Nash published "Wilderness and the American Mind", a work that has become a classic text of early environmental history. In an address to the Organization of American Historians in 1969 (published in 1970) Nash used the expression "environmental history", although 1972 is generally taken as the date when the term was first coined. The 1959 book by Samuel P. Hays, Conservation and the Gospel of Efficiency: The Progressive Conservation Movement, 1890-1920, while being a major contribution to American political history, is now also regarded as a founding document in the field of environmental history. Hays is Professor Emeritus of History at the University of Pittsburgh. Alfred W. Crosby's book The Columbian Exchange (1972) is another key early work of environmental history. Historiography Brief overviews of the historiography of environmental history have been published by J. R. McNeill, Richard White, and J. Donald