Before revision: Since the atmosphere surrounds the earth , which itself is a sphere, the volume of atmosphere bearing on any unit area of the earth 's surface is a truncated cone (which extends from the earth 's center to the vacuum of space; obviously only the section of the cone from the earth 's surface to space bears on the earth 's surface).
After revision: Since the atmosphere surrounds the Earth , which itself is a sphere, the volume of atmosphere bearing on any unit area of the Earth 's surface is a truncated cone (which extends from the Earth 's center to the vacuum of space; obviously only the section of the cone from the Earth 's surface to space bears on the Earth 's surface).