We might take the air we breathe for granted, but the Earth's atmosphere is unique among all the planets. It’s thought that the atmosphere surrounding the Earth has existed since its formation 4.5 billion years ago. However, our atmosphere has developed and changed a lot through time. Without our cherished atmosphere, our planet would be lifeless, baked by the scorching rays and radiation of the Sun during the day and frigidly cold during the night. In this lesson, we will explore some of the things that make our atmosphere so special.
I this lesson we will learn:
Earth’s atmosphere is the layer of gases around the Earth. The atmosphere is held in place by Earth’s gravity.
The atmosphere protects Earth like a big blanket of insulation. It absorbs the heat from the Sun and keeps the heat inside the atmosphere helping the Earth to stay warm - this is called the Greenhouse Effect. It also keeps the Earth's overall temperature fairly steady, especially between night and day. So we don’t get too cold at night and too hot during the day.
There is also a portion of the atmosphere called the Ozone layer, which helps to protect the earth from the Sun’s radiation. This big blanket also helps to form our weather patterns and climate. The weather keeps too much hot air from forming in one place and causes storms and rainfall. All of these things are important to life and the Earth’s ecology.
The atmosphere does not end at a specific place. As you go higher up on the Earth, the atmosphere becomes thinner. There is no clear border between the atmosphere and outer space.
75% of the atmosphere is within 11 kilometers (6.8 miles) of the Earth’s surface.
While oxygen is necessary for most life on Earth, the majority of Earth’s atmosphere is not oxygen.
Earth’s atmosphere is composed of about 78% nitrogen, 21% oxygen, 0.9% argon, and 0.1% other gases.
Trace amounts of carbon dioxide, methane, water vapor, and neon are some of the other gases that make up the remaining 0.1%.
Oxygen is needed by animals to breathe and carbon dioxide is used by plants in photosynthesis.
Solid particulates, including ash, dust, volcanic ash, etc., are small parts of the atmosphere. They are important in making clouds and fog.
The Earth’s atmosphere is divided into five layers (top to bottom):
1. Troposphere – The troposphere is the layer next to the ground or surface of the Earth. It extends to about 20 km (12 miles) above the Earth's surface. This is where we live and even where planes fly. Around 80% of the mass of the atmosphere is in the troposphere. The troposphere is heated by the surface of the Earth.
2. Stratosphere – The stratosphere is the second layer of the atmosphere of the Earth, located above the troposphere and below the mesosphere. The stratosphere layer is 35 km thick. Unlike the troposphere, the stratosphere gets its heat from the ozone layer absorbing radiation from the sun. As a result, it gets warmer the further away you get from the Earth. Weather balloons go as high as the stratosphere.
3. Mesosphere – The mesosphere is directly above the stratosphere and below the thermosphere. It extends from about 50 to 85 km. This is where most meteors burn up upon entry. The coldest place on earth is at the top of the mesosphere.
4. Thermosphere – The thermosphere is next and the air is very thin here. Temperatures can get extremely hot in the thermosphere. This layer is very important in radio communication because it helps to reflect AM radio waves. The International Space Station orbits within the upper part of the thermosphere, at about 320 to 380 km above the Earth.
5. Exosphere - The last layer and the thinnest. It goes all the way to 10,000 km above the Earth’s surface. This is the top layer and merges into interplanetary space.
Where one layer changes to the next to have been named “pauses”. So tropopause is where the troposphere ends. The stratopause is at the end of the stratosphere. The mesopause is at the end of the mesosphere. These are called boundaries.
The Kármán line, or Karman line, is an attempt to define a boundary between Earth's atmosphere and outer space.
Some parts of the atmosphere are hot or cold, depending on height. If an object climbs straight up, it would get colder, but then it would get hotter as the object climbs higher.
The average atmosphere temperature at the Earth's surface is 14°C (57°F).
Troposphere: As the altitude increases, the air temperature decreases. The troposphere is hotter near the Earth’s surface because heat from the Earth warms this air. As the altitude increases, the number of air molecules decreases; thus, the average of their kinetic energy decreases. This result is a decrease in air temperature with an increase in altitude.
Stratosphere: As the altitude increases, the air temperature increases. The stratosphere has a layer of ozone called the ozone layer. This layer absorbs most of the ultraviolet radiation from sunlight. This results in the stratosphere being warmer.
Mesosphere: As the altitude increases, the air temperature decreases. The mesosphere, like the troposphere layer, has a decrease in temperature with altitude because of the decreases in the density of the air molecules.
Thermosphere: As the altitude increases, the air temperature increases. The thermosphere is warmed by the absorption of solar x-rays by the nitrogen and oxygen molecules in this outer layer. Thus, the temperature of this layer increases with altitude.
The atmosphere has pressure. This is because even though the air is gas, it has weight. The average atmospheric pressure at sea level is about 101.4 kilopascals (14.71 psi).
The density of air at sea level is about 1.2 kilograms per cubic meter. This density becomes less at higher altitudes at the same rate that pressure becomes less. The total mass of the atmosphere is about 5.1 × 1018 Kg, which is only a very small part of the Earth’s total mass.
