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Atmosphere, the
Atmosphere, the
Surrounding the Earth is an invisible “envelope” of gases known as the atmosphere. Over time these gases have become sorted into layers, each with a different name and different properties.
The main components of the atmosphere are nitrogen (78%) and oxygen (21%). Other important gases are carbon dioxide and water vapor, although together they make up less than 1% of the atmosphere.
The lowest part of the atmosphere contains the water vapor that helps make our clouds and keep our world warm. Above it are layers containing a gas called ozone that shields us from the harmful ultraviolet rays in space. Further out still, there are layers that allow us to send radio waves around the world.
These are the layers of the atmosphere, beginning at the surface: troposphere; stratosphere; mesosphere; thermosphere; and exosphere.
(The magnetosphere is not part of the atmosphere, but the region around the Earth affected by the Earth’s magnetic attraction.)
 Atmosphere—The atmosphere is the envelope around the Earth that still contains a significant amount of gas. Only the lowest layer, the troposphere, has enough oxygen to support life.
Troposphere (10-20km thick—thickest over the equator, thinnest at the poles). The layer that contains the clouds. It is
mainly transparent to the Sun’s
rays. The temperature decreases with height.
Exosphere (above 600km from the Earth’s surface). Air molecules are very rare at these levels, and helium is the most common gas.
Thermosphere (about 500km thick). Extremely thin air. Readily absorbs ultraviolet radiation. Within this layer lies the ionosphere, the place that bounces back medium (MW) and short (SW) radio waves, allowing them to travel large distances around the world.
Mesosphere (about 50km thick). Transparent to the Sun’s rays. Temperature decreases with height.
Stratosphere (about 30km thick). The air is very “thin” but contains important ozone gas. Temperature increases with height.
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