Atmosphere The lowest layer is the troposphere, which extends from the surface to the bottom of the stratosphere. Three quarters of the atmosphere's mass resides within the troposphere, and is the layer within which the Earth's terrestrial weather develops. The depth of this layer varies between 17 km at the equator to 7 km at the poles. The stratosphere, extending from the top of the troposphere to the bottom of the mesosphere, contains the ozone layer. The ozone layer ranges in altitude between 15 and 35 km, and is where most of the ultraviolet radiation from the Sun is absorbed. The
Day of the Animals claiming that chemical waste released into the atmosphere has dangerously depleted the ozone layer, which protects all life from the sun's radiation. On the mountain, the hikers stumble upon a camp where a fire is burning and coffee cups are ready to be filled, but nobody is around. Steve says the campers will soon be back. He leads the hikers to a nearby spot to bed down for the night. They build a fire, and while Daniel pulls Steve aside to tell him that something strange is going on in the woods. Steve asks him not to say anything to