The atmosphere is a protective layer of gasses that shelters us and all life on Earth.
It comes in distinct layers.
The lowest layer is the troposphere. It stretches from earth's surface to 7 to 12 miles above sea level. The base of this layer is warmer than its top because the air is heated by the surface of the earth, warmed by the sun's energy. Temperatures decrease with height, which is why snow is usually deepest on mountain tops. This is where weather occurs, it is where we live and breath. It's where the air is stirred up and where nearly all of the atmosphere's water vapor and dust particles are found.
Above the troposphere, extending up to about 31 miles, is the stratosphere. Unlike the troposphere, the stratosphere actually gets warmer the higher you go. It's where the ozone layer is found. Ozone molecules absorb high-energy ultraviolet light from the sun, converting the U.V. energy into heat. The stratosphere also lacks the turbulence of the troposphere, which is why commercial airplanes fly there, getting a smoother ride.
Above the stratosphere, extending upward to about 53 miles above the earth's surfaces, is the mesosphere. Here, temperatures grow much colder with height. In fact, the coldest temperatures in the Earth's atmosphere, as low as 130 degrees below zero are found at the top of this layer. The mesosphere is very important for earth's protection, because this is where most meteors and asteroids burn up before reaching earth's surface.
Above the mesosphere, on the edge of space, is the thermosphere. The top of this layer extends up to more than 600 miles above the ground. Molecules here receive extraordinary amounts of energy from the sun, warming with height. A layer of ionized air, called the ionosphere, is found here. This is where auroras happen, the bright, beautiful bands of light that sometimes sees near the poles. This is also where satellites and the International Space Station orbit.
Above the thermosphere is the exosphere, and there's a bit of a controversy with this. Not all scientists agree that the exosphere is really a part of the atmosphere. It's where the uppermost region of the Earth's atmosphere completely fades. There is no clear upper boundary, most agree it tops out about one-half the distance from the Earth to the Moon.
Beyond that, it's all just outer-space.
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What is the atmosphere? 6abc Weather School has the details.
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