Atmosphere of Earth (see the temperature section, below). Because the general pattern of the temperature/altitude profile is constant and measurable by means of instrumented balloon soundings, the temperature behavior provides a useful metric to distinguish atmospheric layers. In this way, Earth's atmosphere can be divided (called atmospheric stratification) into five main layers. Excluding the exosphere, the atmosphere has four primary layers, which are the troposphere, stratosphere, mesosphere, and thermosphere. From highest to lowest, the five main layers are: The exosphere is the outermost layer of Earth's atmosphere (i.e. the upper limit of the atmosphere). It extends from the exobase, which is located at
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