Passage V

As shown in Figure 1, the temperatures of the atmo­spheres of Venus, Earth, and Mars vary with altitude. Figure 1 also shows bow the atmospheric temperature for Earth and Venus varies between day and night and shows the layers of Earth's atmosphere. Table 1 gives the compo­sition of the atmosphere on each planet, both as relative abundance and as the partial pressure, in bars, exerted by each gas at the planet's surface. The total pressure of the gases in Earth's atmosphere at Earth's surface is approxi­mately 1 bar. Table 2 gives what average surface temperatures would be on the 3 planets without greenhouse warming.

Figure and tables adapted from J. Kelly Beatty, Carolyn Collins Petersen, and Andrew Chaikin, The New Solar System, 4th ed. ©1999 by Cambridge University Press.