ATMOSPHERE
The Earth is surrounded by a blanket of air, which we call the atmosphere. It reaches over 560 kilometers (348 miles) from the surface of the Earth, so we are only able to see what occurs fairly close to the ground.  The Atmosphere is a mixture of gases that include water vapor, and dust. Nitrogen and oxygen account for 99 percent of the gases in dry air, with argon, carbon dioxide, helium, neon, and other gases making up the rest. We live in this layer of the Earth. The atmosphere is so spread out that we barely notice it, yet its weight is equal to a layer of water 10.4 meters (34 ft) deep covering the earth. The bottom 30 kilometers (19 mi) of the atmosphere contain about 98 percent of Its mass.
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Our present atmosphere evolved from gases spewed out by early volcanoes. At that time there would have been little or no free oxygen. Oxygen may have been added to the atmosphere by primitive plants during photosynthesis  (see Photosynthesis), Later, more advanced forms of plant life would have added photosynthesis, the process plants use to make food and oxygen out of carbon dioxide and water, may account for most of the oxygen in the atmosphere. Present levels were reached only after millions of years.

The atmosphere acts as a gigantic filter keeping out most ultraviolet radiation while letting the sun's warming rays through to heat the earth and the lower atmosphere. Solar heat is the fuel that makes the atmosphere function as a giant weather machine.