Present-Day Composition

    A. Nitrogen - 78% - Dilutes oxygen and prevents rapid burning at the earth's surface. Living things need it to make proteins. Nitrogen cannot be used directly from the air. The Nitrogen Cycle is nature's way of supplying the needed nitrogen for living things.

    B. Oxygen - 21% - Used by all living things. Essential for respiration. It is necessary for combustion or burning.

    C. Argon - 0.9% - Used in light bulbs.

    D. Carbon Dioxide - 0.03% - Plants use it to make oxygen. Acts as a blanket and prevents the escape of heat into outer space. Scientists are afraid that the buring of fossil fuels such as coal and oil are adding more carbon dioxide to the atmosphere.

    E. Water Vapor - 0.0 to 4.0% - Essential for life processes. Also prevents heat loss from the earth.

    F. Trace gases - gases found only in very small amounts. They include neon, helium, krypton, and xenon.

Table of Contents || Teacher's Guide
History || Composition || Structure
Past, Present, and Future || Oxygen Calculation
Up, Up, and Away || Atmosphere Riddles