Layers of the Atmosphere
Name
Gases that Compose the Atmosphere
The Earth is surrounded by a layer of gases that we call its atmosphere. In
its entirety, the atmosphere consists mainly of nitrogen (78%) and oxygen
(21%). The remaining 1% is made up of much smaller amounts of many
other gases, including argon, carbon dioxide, neon, helium, and
hydrogen. However these gases don’t exist in the same proportions or in
the same mixture or density everywhere in the atmosphere. The Earth’s
atmosphere consists of five main layers, and the gas composition of each
layer is a little bit different.
The exosphere contains the lightest gases in the atmosphere. Hydrogen is
dispersed throughout the exosphere. There is also some helium and
carbon dioxide. Oxygen is found in the part of the exosphere closest to
Earth, near where the exosphere meets the thermosphere. Molecules of
gas in the exosphere are spread very far apart. In the thermosphere, too,
air is extremely thin. There aren’t enough gas molecules here for either
heat or sound waves to travel.
In the next layer closest to Earth, the mesosphere, there is more gas than
there is in the thermosphere, but there is still not enough to be able to
breathe. Meteors tend to burn up as they travel through this layer
because the higher density of gases causes friction and heat.
Just below, the stratosphere has its own set of layers. Here,
gases mix horizontally much more quickly than they mix
vertically, so the coldest, heaviest air sits at the bottom of
the stratosphere and the warmest, lightest air sits at the top.
In the troposphere, the layer closest to the Earth, just the opposite
happens: the higher you go up in the troposphere, the colder the air gets.
In the troposphere, the most important gases are water vapor and carbon
dioxide. The troposphere is where the water cycle and the carbon cycle
take place.
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