Earth’s Atmosphere

The Formation of the Atmosphere

The air you breathe today is made up of 78% nitrogen and 21% oxygen, as well as many other trace gases, like carbon dioxide and water vapor. The atmosphere has not always had the same composition. It has evolved over time since its formation 4.6 billion years ago. In this activity, learn how the atmosphere of the Earth formed and changed over geologic time. Click the player button to begin.

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Composition of Earth’s Atmosphere

The atmosphere of Earth is unique because it contains quite a bit of oxygen, which allows for the various forms of life present on the planet. Have you ever wondered what is in the air you breathe? Air is a word used to describe the mixture of gases in the atmosphere, but which gases make up air? How much of each gas exists in the atmosphere? The pie chart to the right shows the compositions of gases in the atmosphere. The main gas in the atmosphere is nitrogen at 78%. Oxygen makes up roughly 21% of the atmosphere. Argon, carbon dioxide, and trace gases make up the majority of the remaining percentage. Traces gases have a varying percentage in the atmosphere. Trace gases include neon, helium, methane, krypton, hydrogen, methane, and water vapor.

The atmosphere also contains solid components called particulate matter. Particulate matter is composed of solid particles that are suspended in the atmosphere. Natural particulate matter may come from soil, volcanic ash, or salt from the oceans. Humans have caused an increase in particulate matter in the atmosphere from activities such as burning fossil fuels. Water vapor collects on all kinds of particulate matter in the atmosphere, forming clouds. The molecules of gases in the atmosphere do not stay still, rather they move around and can even leave and re-enter the atmosphere through natural cycles such as the water cycle. Even though the individual molecules are often on the move, the atmosphere is still relatively stable in its composition.

Layers of the Atmosphere

Earth’s atmosphere is unique. No other planet in the Solar System has an atmosphere with the correct mixture of gases to support life. Earth’s atmosphere begins at the surface and ends an approximately 300 miles above the surface. Earth's thin atmosphere is divided vertically into layers based on temperature and pressure. Each of these layers has different defining characteristics. View the interactivity to explore the atmospheres different layers. Click the player button to begin.

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Atmospheric Pressure

The layers of the atmosphere are also divided by atmospheric pressure. Air pressure is simply the weight of the air, a force of about 1 kilogram per square centimeter or 14.7 pounds per square inch. Air pressure is measured in millibars (mb) of mercury. The atmospheric pressure at sea level is 1000 mb and decreases with an increase in altitude. The troposphere contains over 50% of all of the air in the atmosphere because the air is more densely packed in this layer. The troposphere has the highest air pressure and each layer contains less density and less air pressure.

Earth's Atmosphere Review

Now that you have investigated Earth's atmosphere, practice what you have learned. In this non-graded activity, drag and drop the words located in the word bank onto the correct space provided on atmospheric layer diagram. Click the player button to get started.