Atmosphere

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. 

The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

Earth's atmosphere can be divided (called atmospheric stratification) into five main layers. From highest to lowest, these layers are:

• Exosphere: >700 km 
• Thermo-sphere: 80 to 700 km (The lower part of the thermosphere, from 80 to 550 km above Earth's surface, contains the ionosphere.)
• Mesosphere: 50 to 80 km 
• Stratosphere: 12 to 50 km 
• Troposphere: 0 to 12 km 

Stratosphere:- 

The ozone layer is contained within the stratosphere.  About 90% of the ozone in our atmosphere is contained in the stratosphere.

Ionosphere:-

The ionosphere is a region of the atmosphere that is ionized by solar radiation. It is responsible for auroras.  It has practical importance because it influences, for example, radio propagation on Earth.

Troposphere:-

Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth's weather takes place.