Weather- March 2017

What Is The Atmosphere

You may have heard people mention the atmosphere before. But do you know what it is? The atmosphere is a layer of gases that surrounds the earth. It contains the air we breathe and all the weather that you see, and it also protects us from outer space.

The atmosphere is made up of many kinds of gases. ere are four gases that are the most common: nitrogen, oxygen, argon and carbon dioxide. You’ve probably heard of oxygen – it’s what we breathe. Oxygen is nearly 21 percent of the atmosphere. Nitrogen is about 78 percent of the atmosphere and is used by living things that need it to make proteins. The other two most common gases, argon and carbon dioxide, are each less than 1 percent of the atmosphere. ere are many other gases as well, but they make up an even smaller percentage of the atmosphere.

The atmosphere stretches out thousands of miles above the earth and consists of ve layers. The first layer, the troposphere, begins at the earth’s surface and is between four and 12 miles high. The difference in height depends on the location on earth – near the equator, the troposphere is the highest, while it is lowest at the poles. e troposphere is where almost all weather occurs.

On top of the troposphere is the next layer, the stratosphere. It goes up to about 31 miles above the earth. is layer is hotter than the troposphere, and the temperature increases along with the height.

Above the stratosphere is the mesosphere, which reaches to about 53 miles above the earth. is layer of the atmosphere protects us from meteors falling down to Earth. This is because the gases in this layer are much denser, which causes meteors to slow down and burn up.

e next layer up is the thermosphere, also known as the upper atmosphere. is layer extends to about 375 miles above the earth. Above that is the exosphere, which reaches up to 6,200 miles above the earth. A er that is outer space.

Water is continuously circulated between the earth and the atmosphere. is is known as the hydrologic cycle. Water repeatedly moves from the ground to the atmosphere and back again. The hydrologic cycle consists of five main processes: evaporation, transpiration, condensation, precipitation and runoff.

Evaporation is when liquid changes into a gaseous form known as water vapor. Water evaporates, rising up into the atmosphere. Transpiration is similar to evaporation, except it occurs with plants. Condensation is when water vapor transforms back into liquid in the atmosphere. is o en appears as clouds. Precipitation is when the tiny condensation particles grow too large, and then fall back down to earth — also known as rain. When the water falls back down to earth, some is absorbed into the ground, and the rest is known as runo , which forms lakes and rivers. Eventually, some of the water in these lakes and rivers evaporates, beginning the process all over again.

For more information on the atmosphere and other cool weather facts, check out the Jetstream, the National Weather Service’s online school for weather, located at:

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