Measuring approximately eleven kilometers high, the troposphere is the bottom-most layer of the atmosphere and the closest to the surface of Earth. In addition, all of Earth’s weather takes place in this layer, which is bonded on the top by an additional layer of air called the tropopause. The troposphere’s most prevalent gases include 78 percent nitrogen, 21 percent oxygen and one percent argon.
The troposphere contains seventy-five percent of the atmosphere’s mass as well as the majority of the atmosphere’s water vapor, which ranges from trace amounts in the Polar Regions to nearly four percent in the tropics. Water vapor plays a significant role in regulating air temperature, due to its absorption of solar energy and thermal radiation from Earth’s surface. Weather occurs only in the troposphere as a result of the high amounts of water vapor contained here. The troposphere is the most unstable layer, as the air is in constant and regular motion.
Above the troposphere is the layer known as the stratosphere. This is also the layer where jet airplanes fly in order to avoid the turbulence which takes place in the troposphere. The top of the stratosphere occurs at fifty kilometers in altitude. The boundary between the stratosphere and the mesosphere above is called the stratopause. Ozone, a type of oxygen molecule that is abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun.
The stratosphere is extremely dry and contains very little water vapor. The air is also thin and does not contain the movement of the troposphere. Due to the lack of vertical convection in the stratosphere, materials that come into the stratosphere can remain there for long periods of time. Ozone destroying chemicals called chlorofluorocarbons (CFCs) are one such example. In addition, volcanic eruptions and meteorite impacts can propel aerosol particles up into the stratosphere where they linger for months or years, altering Earth’s global climate.
The mesosphere is located directly above the stratosphere, beginning at 50 kilometers above Earth’s surface. The mesopause is the boundary which separates the mesosphere and the thermosphere above. This layer has proven difficult for scientists to conduct research, as weather balloons and airplanes are not able to reach the mesosphere.
This region of the atmosphere is characterized by strong zonal winds, atmospheric tides, internal atmospheric gravity waves, and planetary waves. This is also the location in which meteors from space burn as a result of a collision with particular gas particles. The mesosphere is home to a distinct type of cloud called “noctilucent cloud,” which forms in the mesosphere near the North and South Poles. There is also lightning in the mesosphere which is commonly referred to as “sprites.”
The thermosphere extends from approximately 90 kilometers to between 500 and 1,000 kilometers above the Earth. Temperatures in the thermosphere range from nearly 500° C (932° F) to 2,000° C (3,632° F). The thermopause is the boundary between the thermosphere and the exosphere. Although the thermosphere is generally considered to be part of Earth’s atmosphere, the air density is extremely low in this particular layer; therefore, the majority of thermosphere is often thought of as outer space.
Air in the lower part of the thermosphere is primarily composed of 80 percent nitrogen and 20 percent oxygen. In the upper thermosphere, atomic oxygen, atomic nitrogen, and helium comprise the main elements of air. The thermosphere absorbs a large amount of the X-ray and UV radiation from the sun. In addition, the aurora (the Southern and Northern lights) occurs in the thermosphere.
The exosphere is the top most region of Earth’s atmosphere. The layer below the exosphere is the thermosphere and the boundary which separates these two layers is called the thermopause. Since this portion of the Earth’s atmosphere gradually extends into space, there is no established boundary separating the exosphere from outer space. Many scientists consider this layer a part of space rather than the Earth’s atmosphere. Satellites such as the International Space Station (ISS) orbit within the exosphere. Although the atmosphere contains extremely thin air, there is still enough air and movement to cause a slight amount of drag force exerted upon satellites that orbit within these layers.
Composition of the Atmosphere