Robin Hopper, age 13, of Austin, Tex., for her question:
WHAT IS THE WORLD'S ATMOSPHERE LIKE?
Atmosphere is the air which surrounds the earth. Scientists divide it into four layers: the troposphere, the stratosphere, the mesosphere and the thermosphere.
Atmosphere is also a measure of atmospheric pressure. An atmosphere is a pressure 14.7 pounds per square inch of surface. This reading is taken at sea level.
Air surrounds the earth and goes up above it as far as 1,000 miles. Nitrogen makes up 78 percent of the atmosphere and oxygen makes up about 21 percent. The remaining 1 percent is made up mainly of argon and small amounts of other gases. It also contains some water vapor and particles of dust.
Clouds float in the lowest part of the atmosphere, which we call the troposphere. Most storms also occur here. Temperature drops rapidly as the altitude increases. The troposphere continues up for about 10 miles.
Above the troposphere is the stratosphere, which continues upward for about 30 miles. It is here that the jet planes fly. Near the top of the layer, the temperature is about 28 degrees Fahrenheit.
Next up, and continuing for about 50 miles, is the mesosphere where trails left by meteors appear. Temperatures here are minus 135 degrees Fahrenheit.
More than 99 percent of all air is below the earth's highest layer, the thermosphere. The sun's heat brings the temperature of the thin air here to a sizzling 2,700 degrees Fahrenheit.
The ionosphere is a region of electrically charged particles which is centered in the lower thermosphere and extends upward for several hundred miles. The ionosphere plays an important part in radio communications. Radio waves that bounce off it can travel far around the earth.
Air pressure at an altitude of 10,000 feet is 10.2 pounds per square inch, with it dropping to 6.4 pounds per square inch at 20,000 feet and 1.6 pounds at 50,000 feet.
The exosphere is the portion of the thermosphere above the ionosphere. It contains so little air that there is almost no resistance there to satellites or spacecraft orbiting the earth.
Because the exosphere is the outermost region of the earth's atmosphere, it is from there that molecules escape into outer space.
Air doesn't have color, smell or taste. Yet it is just as real as land or water. You don't usually see it because it is transparent.
You can feel air against your face when the wind blows and you can see tree branches and plants move as air pushes against them. Most sounds come to us through the air.
Air has weight and it also shows resistance to any motion.