A diagram showing the density of the Earth's atmosphere. The atmosphere is densest near the surface of teh Earth. This can be seen by the closey packed molecules near the surface of the earth in the inset images. In comparison, the molecules become more loosely packed as one moves away from the Earth's surface. This can be seen from the inset images. The important levels are also shown:

• Washington D.C. is at 9 m
• Denver, Colorado is at 1600 m
• Mexico City is at 2240 m
• Mount Kilimanjaro in Africa is at 5963 m
• Mount McKinley in Alaska is at 6194 m
• Mount Everest in Asia is at 8848 m
• The standard cruising altitude for jet liners is 10,000 to 12,000 m