2. The Earths Atmosphere Some numbers. Weight: 5.7x1015 tons, one-millionth the weight of the earth Area: 200 million square miles Thickness: hundreds of miles Half of the air is below 18.000 feet altitude above see level Density at sea level: 1.3 kg/m3 Pressure at sea level: 14.7 lb/in2(1.01x105 N/m2) The density and the corresponding pressure, gradually decrease with altitude By 50,000 feet the pressure has been reduced to 1.6 Ib/in,, and by 600 miles altitude the atmospheric pressure is essentially zero2. The Earth’s Atmosphere Some numbers: • Weight: 5.7x1015 tons, one-millionth the weight of the earth. • Area: 200 million square miles. • Thickness: hundreds of miles. Half of the air is below 18,000 feet altitude above see level. • Density at sea level: 1.3 kg/m3 . • Pressure at sea level: 14.7 lb/in2 (1.01x105 N/m2 ) The density and the corresponding pressure, gradually decrease with altitude. By 50,000 feet the pressure has been reduced to 1.6 lb/in2 , and by 600 miles altitude the atmospheric pressure is essentially zero