3.2: The Atmosphere

The Atmosphere

The atmosphere is a gaseous mass or envelope surrounding the Earth, and retained by the Earth's gravitational field. The Earth's atmosphere is subdivided into levels:

* The troposphere is the lowest portion (up to about 6-8 miles [10-13 km]) where all weather takes place and contains about 80% of the atmosphere's mass and 99% of its water vapor.

* The overlying stratosphere extends up to about 31 miles (50 km). It contains an abundance of ozone which absorbs ultraviolet radiation, protecting life on land and in the shallow ocean .

*The mesosphere is the part of the earth's upper atmosphere above the stratosphere in which temperature decreases with altitude to the atmosphere's absolute minimum.

* The thermosphere the region of the atmosphere above the mesosphere and below the height at which the atmosphere ceases to have the properties of a continuous medium (about 60 miles [100 km]). The thermosphere is characterized throughout by an increase in temperature with height. Here where the charged atomic particles of the solar wind interacts with atmospheric gases.

Figure 3.3. Structure of the Earth's atmosphere.