The Atmosphere can be defined as the gaseous envelope surrounding the earth.
Atmosphere can also be defined as a grand body from the earth surface to the outer space and composed of number of gases.
The estimated mass of the atmosphere is 5.6 × 1014 metric tonnes. It extends over about 400 km height and meteorological events and effects occur in it. The thickness of the gaseous envelope is equal to 1% of the earth’s mean radius.
The usefulness of the atmosphere:
- It fulfills the biological oxygen demand (BOD) of animal life.
- It supplies the necessary precipitation or moisture.
- It protects the biological life on the planet from harmful extraterrestrial radiations like UV, by absorbing it through the ozone.
- It maintains the warmth of the planet through its greenhouse effect, avoiding the temperature to fall to two extreme limits.(The earth’s temperature in the absence of an atmosphere would have been +950C (day), and -1450C (Night)
- It provides the necessary CO2 which is the basic input required to run the photosynthesis process in plants to build biomass.
- It provides the necessary medium for the transport of pollen. Seed spores and insets. Many physical-chemical and hydrological processes responsible for weather and climate occur in the atmosphere only.
- The atmosphere is a big reservoir of nitrogen. Some plants and microbes can fix this nitrogen for plant growth e.g., Azolla pinara Azotobacter.