CSET Requirement 2.3 a: Compare the layers of the atmosphere in terms of chemical composition and thermal structure.
Chemical and Thermal Structure
The Troposphere is the lowest layer of the atmosphere and measures about 7 miles(12 km). It contains over 75 percent of all the atmosphere's gases and vast quantities of water and dust. As the sun heats the ground, it keeps this thick mixture churning. The weather is caused by these churnings of the mass. The troposphere is normally warmest at ground level and cools higher up where it reaches its upper boundary (the tropopause). The tropopause (boundary between troposphere and stratosphere) varies in height. At the equator it is at 11.2 miles(8 km) high, at 50 N and 50 S, 5.6 miles(9 km) and at the poles 3.7 miles(6 km) high.
The troposphere is 70% Nitrogen and 21% Oxygen. The lower density of molecules higher up would not give us enough to survive.
The Stratosphere extends from the tropopause up to its boundary (the Stratopause), 31 miles(50 km) above the Earth's surface. In this layer there is 19 percent of the atmosphere's gases and it contains little water vapour. Compared to the troposphere it is calm in this layer. The movements of the gases are slow. Within the stratosphere is the ozone layer, a band of ozone gas, that absorbs harmful ultraviolet rays of the sun. The higher you get in the atmosphere, the warmer the air gets. The temperature rises from -76 ºF(-60 ºC) at the bottom to a maximum of about 5 ºF(10 ºC) at the stratopause. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Because of this temperature stratification, there is little convection and mixing in the stratosphere, so the layers of air there are quite stable. Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below. Ozone an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun.
The Mesosphere is the next layer above the stratopause and extends to its upper boundary (the Mesopause), at 50 miles(80 km) above the ground. The gases in the mesosphere are too thin to absorb much of the sun's heat, but thick enough to slow down meteorites hurtling into the atmosphere. They burn up, leaving fiery trails in the night sky. The temperatures in the mesosphere drop to -130 ºF(-90 ºC) at the mesopause.
The Thermosphere is the layer above the mesopause. The gases of the thermosphere are even thinner than those in the mesosphere, but they absorb ultraviolet light from the sun. Because of this, the temperatures rise to 3,600 ºF (2,000 ºC) at the top. This is at a height of 430 miles (700 km) of the earth's surface. In the thermosphere is a separate layer, the Ionosphere. This layer extends of 62 miles(100 km) to 190 miles(300 km) of the earth's surface. It is made of electrically charged gas particles (ionised). The particles get this electric charge by ultraviolet rays of the sun. The ionosphere has the important quality of bouncing radio signals, transmitted from the earth. That’s why places all over the world can be reached via radio. The thermosphere is the layer where Auroras tend to occur.
The Exosphere is the outermost layer of the atmosphere and extends from 430 miles(700 km) to 500 miles(800 km) above the ground. In this layer gases get thinner and thinner and drift off into space. The main gases within the exosphere are the lightest gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen near the exobase. Since there is no clear boundary between outer space and the exosphere, the exosphere is sometimes considered a part of outer space. The upper boundary of the exosphere can be defined theoretically by the altitude about 190,000 kilometres (120,000 mi), half the distance to the Moon, at which the influence of solar radiation pressure on atomic hydrogen velocities exceeds that of the Earth’s gravitational pull. The exosphere observable from space as the geocorona is seen to extend to at least 100,000 kilometres (62,000 mi) from the surface of the Earth. The exosphere is a transitional zone between Earth’s atmosphere and interplanetary space. The exosphere is almost a vacuum. The "air" is very, very thin there. When air is thin, it doesn't transfer much heat to objects in the air, even if the air is very, very hot. However, the exosphere would feel quite cold to us. Since the "air" is so thin in the exosphere - it is almost a vacuum - there are very, very few particles. We feel warmth when particles hit our skin and transfer energy to us. There are too few particles in the exosphere to transfer much energy, even though each particle is quite "hot" itself.
The Stratosphere extends from the tropopause up to its boundary (the Stratopause), 31 miles(50 km) above the Earth's surface. In this layer there is 19 percent of the atmosphere's gases and it contains little water vapour. Compared to the troposphere it is calm in this layer. The movements of the gases are slow. Within the stratosphere is the ozone layer, a band of ozone gas, that absorbs harmful ultraviolet rays of the sun. The higher you get in the atmosphere, the warmer the air gets. The temperature rises from -76 ºF(-60 ºC) at the bottom to a maximum of about 5 ºF(10 ºC) at the stratopause. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Because of this temperature stratification, there is little convection and mixing in the stratosphere, so the layers of air there are quite stable. Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below. Ozone an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun.
The Mesosphere is the next layer above the stratopause and extends to its upper boundary (the Mesopause), at 50 miles(80 km) above the ground. The gases in the mesosphere are too thin to absorb much of the sun's heat, but thick enough to slow down meteorites hurtling into the atmosphere. They burn up, leaving fiery trails in the night sky. The temperatures in the mesosphere drop to -130 ºF(-90 ºC) at the mesopause.
The Thermosphere is the layer above the mesopause. The gases of the thermosphere are even thinner than those in the mesosphere, but they absorb ultraviolet light from the sun. Because of this, the temperatures rise to 3,600 ºF (2,000 ºC) at the top. This is at a height of 430 miles (700 km) of the earth's surface. In the thermosphere is a separate layer, the Ionosphere. This layer extends of 62 miles(100 km) to 190 miles(300 km) of the earth's surface. It is made of electrically charged gas particles (ionised). The particles get this electric charge by ultraviolet rays of the sun. The ionosphere has the important quality of bouncing radio signals, transmitted from the earth. That’s why places all over the world can be reached via radio. The thermosphere is the layer where Auroras tend to occur.
The Exosphere is the outermost layer of the atmosphere and extends from 430 miles(700 km) to 500 miles(800 km) above the ground. In this layer gases get thinner and thinner and drift off into space. The main gases within the exosphere are the lightest gases, mainly hydrogen, with some helium, carbon dioxide, and atomic oxygen near the exobase. Since there is no clear boundary between outer space and the exosphere, the exosphere is sometimes considered a part of outer space. The upper boundary of the exosphere can be defined theoretically by the altitude about 190,000 kilometres (120,000 mi), half the distance to the Moon, at which the influence of solar radiation pressure on atomic hydrogen velocities exceeds that of the Earth’s gravitational pull. The exosphere observable from space as the geocorona is seen to extend to at least 100,000 kilometres (62,000 mi) from the surface of the Earth. The exosphere is a transitional zone between Earth’s atmosphere and interplanetary space. The exosphere is almost a vacuum. The "air" is very, very thin there. When air is thin, it doesn't transfer much heat to objects in the air, even if the air is very, very hot. However, the exosphere would feel quite cold to us. Since the "air" is so thin in the exosphere - it is almost a vacuum - there are very, very few particles. We feel warmth when particles hit our skin and transfer energy to us. There are too few particles in the exosphere to transfer much energy, even though each particle is quite "hot" itself.