Notes

Layer of the atmosphere

There are molecules of over eight different kinds of gases in the atmosphere with nitrogen being the most abundant.

Also in the atmosphere are water vapor small and liquid and solid particles.

Observation over time and advances in technology have shown that the atmosphere is made with several distinct layers

The layers are are classified by difference in temperature air pressure and density

Layers of the Atmosphere
Spacecraft traveling around Earth often take pictures of the planet from space. In this picture, you can see a thin, blue layer wrapped like a blanket around Earth.

Life depends on the gases in this layer. Earth’s gravity holds this layer close to the planet. Beyond this layer lies the cold darkness of space. What are some of the features of this layer?
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The atmosphere actually begins at the surface of the ground. Each time you step out the door, you step into the atmosphere – at least into its first layer. If you fly to a destination, you are likely flying through this same layer of the atmosphere. This first layer is called the troposphere, and it extends to about 7 miles or 11.3 km above

Curiosity about the atmosphere probably began as soon as humans realized clouds signaled rain. Ancient cultures used the sky to determine drought and flood seasons. In the fifteenth century, motions of the stars were used to predict weather. In the late 1800s, scientists even risked their own lives to find out about the atmosphere.

Composition of the Atmosphere
What is the atmosphere made of? Gas! There are molecules of over eight different kinds of gases in the atmosphere with nitrogen being the most abundant. Also in the atmosphere are water vapor and small liquid and solid particles.

Observations over time and advances in technology have shown that the atmosphere is made of several distinct layers. The layers are classified by differences in temperature, air pressure, and density. The lowest layer, extending just seven miles from Earth’s surface, contains all the weather you experience and the air you breathe.
Differences in Density
This is a diagram showing the layers of the atmosphere. The layers are defined by their height, or altitude , above Earth’s surface.

Recall that density measures the number of molecules in a certain amount of space, or volume. Look at each layer of the atmosphere to compare their molecules. What do you notice?

The bottom layers contain more gas molecules than the top. The layer closest to Earth, the troposphere , is more dense than any other layer. The very thin air of the exosphere is the least dense. The exosphere is the last layer of the atmosphere. Gases in the exosphere can escape Earth's atmosphere and go into space.
Air Pressure
Even though you can't see it, air is matter and has weight. Gravity pulls it down, and it presses on everything underneath it.

Imagine a stack of books. The bottom book experiences the most pressure from the books on top, and the topmost books experience the least amount of pressure. This is similar to the pressure in the atmosphere, where the bottom layers undergo the highest amount of air pressure from the layers on top, and the top layers experience less air pressure. Notice how air pressure decreases sharply in the troposphere and then stays very low throughout the rest of the atmosphere's layers.

Temperature
While density and air pressure both decrease with altitude, temperature fluctuates or rises and falls. As you read, use the slider to see how temperature changes throughout each layer
In the troposphere, temperature falls at higher altitudes where fewer molecules are available to transfer heat.
Gases in the stratosphere absorb radiation from the sun, so temperatures rise.
Temperatures drop in the mesosphere, the coldest atmospheric layer.
Temperatures rise in the thermosphere due to absorption of energy from the sun. However, with so much space between so few molecules, it does not feel warm.

Activity in the Atmosphere
At any given time of day or night, there is activity in the atmosphere. In the troposphere where weather occurs, it may be clear skies in one part of the world, while in another place, a plane is navigating through turbulence caused by wind or clouds.

Weather balloons may be recording data in the stratosphere , while meteorites above burn up from friction in the mesosphere . In the thermosphere, charged particles trapped in Earth’s magnetosphere produce spectacular aurora , known as the northern lights in the northern hemisphere. Satellites or even a space shuttle are in orbit. But most important is the constant protection provided by the atmosphere for life on Earth.

A very important gas called ozone can be found in the stratosphere. Ozone absorbs rays of damaging ultraviolet (UV) light coming from the sun. In large doses, ultraviolet rays can harm skin, causing sunburns, aging, and skin cancer. UV light can also damage eyes.

A very important gas called ozone can be found in the stratosphere. Ozone absorbs rays of damaging ultraviolet (UV) light coming from the sun. In large doses, ultraviolet rays can harm skin, causing sunburns, aging, and skin cancer. UV light can also damage eyes.

Recent data shows that some destruction of the ozone layer has been caused by manmade chemicals called chlorofluorocarbons , or CFCs. With less ozone in the stratosphere, more harmful UV rays can reach Earth’s surface.