What Are the Three Most Abundant Gases in the Earth's Atmosphere? | The Classroom | Synonym
What Are the Three Most Abundant Gases in the Earth's Atmosphere?
by Chris Deziel
There is no discrete boundary between Earth's atmosphere and space.
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The layer of gases that surrounds Earth and forms its atmosphere is paper-thin when compared with the diameter of the planet itself, and without it, life probably wouldn't exist. Besides providing the necessities for respiration, the atmosphere filters dangerous rays from the sun while trapping warmth and preventing it from radiating into space. Two molecules form the bulk of the atmosphere, while trace amounts of several others make up the rest.
The 2 Main Components
As Earth was forming, volcanoes spewed ammonia, carbon dioxide and water vapor into the atmosphere. Much of the carbon dioxide dissolved in seawater, and nitrogen, which is a component of ammonia, now forms 78 percent of the atmosphere. As the planet matured, organisms in the seawater learned to live on carbon dioxide, expelling oxygen gas -- which comprises two oxygen molecules bonded together -- as a waste product. Consequently, oxygen forms 21 percent of the atmosphere. Oxygen is actually 10,000 times more abundant on Earth than nitrogen because it forms stable lattices with other elements and is incorporated into the ground.
The 1 Percent
The last 1 percent of the gases in the atmosphere form two groups: those whose quantities fluctuate and those that remain constant. The most abundant of these trace components is argon, which forms a constant 0.93 percent of the atmosphere. Other noble gases -- helium, neon and krypton -- also exist in trace amounts. Among the elements whose quantities vary are water vapor, ozone, methane, sulfur dioxide, nitrogen oxides and -- most abundantly -- carbon dioxide. The atmosphere also contains particulate matter, such as snow, dust and volcanic ash, whose quantities are highly variable.
Importance of Variable Components
The main components of the atmosphere -- nitrogen and oxygen -- don't have much effect on the meteorological patterns or climate, but the variable elements do. For example, variations in water vapor reflect relative humidity. The so-called greenhouse gases -- carbon dioxide, sulfur dioxide, methane and nitrogen oxide -- absorb heat from the Earth and warm the planet. Without these gases in the atmosphere, the average temperature of the earth would be 30 degrees Celsius (54 degrees Fahrenheit) cooler than it is now, and current life forms probably wouldn't exist.
Learning from Other Planets
Saturn's moon Titan has an atmosphere that resembles what scientists believe once existed on Earth. It is composed almost entirely of nitrogen, but has small amounts of methane and other hydrocarbons. By studying this atmosphere and the effect that sunlight has upon it, scientists hope to gain an understanding of how life developed on primordial Earth. The planet Venus, on the other hand, offers a dramatic demonstration of the effects of greenhouse gases. The presence of large amounts of carbon dioxide and sulfur dioxide in the atmosphere of that planet has produced a runaway warming effect that has raised the surface temperature to 460 degrees Celsius (860 degrees Fahrenheit).
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