The Earth’s Atmosphere
5
An invisible blanket of gases called the atmosphere surrounds the Earth. Air is one of the main elements that makes life on Earth possible. Air, which makes ups the Earth’s atmosphere is made up of a variety of gases and other particles. The most abundant gas in the Earth’s atmosphere is nitrogen.
4
Nitrogen (N
2
) composes 78% of the atmosphere. Oxygen (O
2
) makes up about 21% and Argon (Ar) is about 0.9%. The remaining 0.1% is made up of water vapor, carbon dioxide (CO
2
), methane (CH
4
), nitrous oxide (NO
2
), ozone (O
3
), and hydrogen.
4
The Earth’s atmosphere extends outward to approximately 6,000 miles and the atmosphere changes as you go further from the Earth’s surface. However, the majority of that atmosphere is compressed into the first 16 miles. The further up into the atmosphere you go the less compressed the atmosphere becomes because there is less pressure being exerted.
5
Layers of the Atmosphere
5
In order to better understand our atmosphere scientists have divided it into several layers. These layers are named based on the characteristics of the gases found at that height and their temperatures. They resemble a layered cake and each layer in our atmosphere is a sphere covering the entire Earth. Air pressure, or the weight of the air above a given location, is greatest at the Earth’s surface. For example, at sea level, molecules of air are packed close together. Air pressures decreases though as one moves upward into the atmosphere. So the air molecules outside of an airplane are further apart. Some layers contain gases that readily absorb the sun’s energy, while others do not. The five many laser of the Earth’s atmosphere include the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
The first layer of the atmosphere is made out of the gases that we breathe everyday and is closest to the ground. This layer is called the troposphere. On average the troposphere extends from the surface of the Earth upwards to a height of 7 miles. The troposphere is the layer that we live in and where all weather occurs. It contains almost all of the Earth’s carbon dioxide, water vapor, air pollution, weather, clouds, and living things. The temperatures in this layer are warmest at the surface of the Earth and they decrease higher in the troposphere. The troposphere is unique in that it receives convective heat transfer, where all other layers transport heat through radiation. There is also no water vapor at higher layers in the atmosphere because water is frozen out at the troposphere.
11
The next layer of our atmosphere is called the stratosphere. The air here is very thin and contains little moisture. Air in the lower stratosphere is very cold. At the top of this layer a thin layer of ozone is found. The ozone layer helps to protect Earth from the sun’s harmful ultraviolet (UV) radiation by absorbing it. And temperatures near the ozone layer are warmer as a result.
Above the stratosphere lies the mesosphere, the middle layer of the atmosphere. This layer is the coldest layer. And it is also where meteors falling to the Earth often burn up, which can cause métier showers.
Next, lies the thermosphere. Air here is extremely thin and temperature increases with altitude. The thermosphere is composed of a sub-layer to the atmosphere called the ionosphere. The ionosphere contains particles that have become electrically charged by the sun’s energy. Beautiful displays of colors in the night sky, called auroras, occur here.
The final layer or outermost layer of the atmosphere is the exosphere. Some satellites, such as the International Space Station actually orbit the Earth here. Beyond the exosphere lies outer space.
Even though scientists have given special names to the boundary between each layer, this does not mean that there is an actual clearly visible border. If you were traveling up through the atmosphere in a rocket ship, you would not see any sudden changes as you went from one layer to the next. Instead, the change is gradual. The troposphere slowly changes, mixing with the stratosphere. The higher you travel the less and less the air around you will resemble the air found in the troposphere and the more and more it will resemble the air found in the stratosphere.
Figure 1. Earth's atmosphere by Kelvinsong - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.
7
The Ozone Layer
5
An important gas in the stratosphere and mesosphere is ozone. Ozone is a molecule made up of three oxygen atoms. This gas is mainly found in a layer of the atmosphere commonly referred to as the ozone layer. The ozone layer is found approximately 9 miles above the surface of the Earth, and continues onward to about 30 miles above Earth’s surface.
5
The ozone is formed by interactions of ultraviolet radiation in sunlight with oxygen. This gas has the unique ability to absorb the Sun’s ultraviolet radiation. Like a giant sheet of sunscreen it protects humans, animals, and plants from getting too much of the Sun’s brutal ultraviolet rays. Without this protection conditions on this planet would become very hazardous.
5