Atmosphere of Earth However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft. The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about , although this altitude varies from about at the geographic poles to at the Equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e. a layer of
Before We Ruled the Earth 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 part in the series shows how humans started out as prey for other