Atmosphere of Earth relatively warm air above a colder one), and in others by a zone which is isothermal with height. Although variations do occur, the temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth's surface) is typically the warmest section of the troposphere. This promotes vertical mixing (hence, the origin of its name in the Greek word τρόπος, "tropos", meaning "turn"). The troposphere contains roughly 80% of the mass of Earth's atmosphere. The troposphere is denser than all its overlying atmospheric
Before We Ruled the Earth Aurochs, Woolly mammoth, Tundra wolf, Paleo-Indian, "Megalonyx jeffersoni", "Homo sapiens", and American buffalo. Before We Ruled the Earth Before We Ruled the Earth is a two-part documentary television miniseries that premiered on February 9, 2003 on the Discovery Channel. The program featured early human history and the challenges human beings faced thousands of years ago. It also features animals examples such as: Woolly mammoth, "Megantereon", American buffalo, cave bear, and Irish elk ("Megaloceros giganteus"). The first episode was called "Hunt or Be Hunted" and the second called "Mastering the Beasts." "Hunt or Be Hunted" (narrated by Linda Hunt). The first