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The envelope of gas surrounding our planet Earth, known as the atmosphere, is organized into five distinct layers. These layers start at ground level, measured at sea level, and rise into what we call outer space. From the ground up they are:
- the troposphere,
- the stratosphere,
- the mesosphere,
- the thermosphere, and
- the exosphere.
In-between each of these major five layers are transition zones called "pauses" where temperature changes, air composition, and air density occur. Pauses included, the atmosphere is a total of 9 layers thick!
The Troposphere: Where Weather Happens
Of all the atmosphere's layer's, the troposphere is the one we're most familiar with (whether you realize it or not) since we live at its bottom -- the Earth's surface. It hugs the Earth's surface and extends upward to about high. Troposphere means, 'where the air turns over'. A very appropriate name, since it is the layer where our day-to-day weather takes place.
Starting at sea level, the troposphere goes up 4 to 12 miles (6 to 20 km) high. The bottom one third, that which is closest to us, contains 50% of all atmospheric gasses. This is the only part of the whole makeup of the atmosphere that is breathable. Thanks to its air being heated from below by the earth's surface which absorbs the sun's heat energy, tropospheric temperatures decrease as you travel up into the layer.
At its top is a thin layer called the tropopause, which is just a buffer between the troposphere and the stratosphere.
The Stratosphere: Ozone's Home
The stratosphere is the next layer of the atmosphere. It extends anywhere from 4 to 12 miles (6 to 20 km) above Earth's surface up to 31 miles (50 km). This is the layer where most commercial airliners fly and weather balloons travel to.
Here the air doesn't flow up and down but flows parallel to the earth in very fast moving air streams. It's temperature also increases as you go up, thanks to the abundance of natural ozone (O3) -- the byproduct of solar radiation and oxygen which has a knack for absorbing the sun's harmful UV rays. (Anytime temperatures increase with elevation in meteorology, it's known as an "inversion.")
Since the stratosphere has warmer temperatures at its bottom and cooler air at its top, convection (thunderstorms) is rare in this part of the atmosphere. In fact, you can visibly spot its bottom layer in stormy weather by where the anvil-shaped tops of cumulonimbus clouds are. How so? Since the layer acts as a "cap" to convection, the tops of storm clouds have nowhere to go but spread outward.
After the stratosphere, there is again a buffer layer, this time called the stratopause.
The Mesosphere: The "Middle Atmosphere"
Starting roughly 31 miles (50 km) above Earth's surface and extending up to 53 miles (85 km) is the mesosphere. The mesosphere's top region is the coldest naturally occurring place on Earth. Its temperatures can dip below -220 °F (-143 °C, -130 K)!
The Thermosphere: The "Upper Atmosphere"
After the mesosphere and mesopause come the thermosphere. Measured between 53 miles (85 km) and 375 miles (600 km) above the earth, it contains less than 0.01% of all air within the atmospheric envelope. Temperatures here reach upward to 3,600 °F (2,000 °C), but because the air is so thin and there are so few gas molecules to transfer the heat, these high temperatures would amazingly feel very cold to our skin.
The Exosphere: Where Atmosphere and Outer Space Meet
Some 6,200 miles (10,000 km) above the earth is the exosphere -- the atmosphere's outer edge. It is where weather satellites orbit the earth.
What About the Ionosphere?
The ionosphere isn't its own separate layer but is actually the name given to the atmosphere from about 37 miles (60 km) to 620 miles (1,000 km) high. (It includes the top-most parts of the mesosphere and all of the thermosphere and exosphere.) Gas atoms drift into space from here. It is called ionosphere because in this part of the atmosphere the sun's radiation is ionized, or pulled apart as it travels earth's magnetic fields to the north and south poles. This pulling apart is seen from earth as auroras.
Edited by Tiffany Means