What Is the Most Common Chemical Element Found in the Earth's Atmosphere?

Earth's early atmosphere was very different from that of today.

Earth's atmosphere consists of four layers--the troposphere, stratosphere, mesosphere and ionosphere--that extend about 400 kilometers (about 250 miles) from the earth's surface. The bottom 30 kilometers (about 20 miles), however, contain almost 97 percent of all of the gas molecules in the atmosphere.

Early Atmosphere

Earth's early atmosphere probably consisted mostly of hydrogen and helium, similar to the so-called "gas giants," such as Jupiter. Earth, however, lacked sufficient mass to produce enough gravity to hold these gases near the surface, and they eventually evaporated into space.

Second Atmosphere

Volcanic outgassing produced many of the current atmospheric components, including nitrogen, carbon dioxide and water vapor, all of which are substantially "heavier" than hydrogen or helium. Volcanic gases, however, do not contain oxygen. Virtually all of the atmospheric oxygen was later produced by plants.

Atmospheric Composition

Today, just two elements--nitrogen and oxygen--comprise 99 percent of the atmosphere. Nitrogen alone accounts for 78 percent. Other trace gases include argon, at 0.93 percent, and carbon dioxide, at about 0.04 percent.

References

• University of Tennessee-Knoxville: The Earth's Atmosphere
• Eastern Illinois University: Origin of the Earth's Atmosphere

Resources

• University of Wisconsin Stevens Point: The Atmosphere
• University Corporation for Atmospheric Research: Introduction to the Atmosphere