Atmosphere of Earth and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft. The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly above Earth's surface to the stratopause at an altitude of about . The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of
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