(i) Atmosphere is an envelope of gases surrounding the earth or any other planet. Nitrogen, oxygen, and other gases are present in the earth’s atmosphere. It is divided into a number of layers.

(ii) The elements of weather and climate are temperature, pressure, winds, humidity, clouds and precipitation. These elements are subject to change and influence human life on Earth.

(iii) The atmosphere is composed of gases, water vapour and dust particles. Nitrogen constitutes about 78-79%, oxygen constitutes about 20-21% and other gases like carbon dioxide, helium, hydrogen, methane constitute about remaining 1%.

(iv) Troposphere is the most important of all the layers of the atmosphere because-

• Most of the weather phenomena take place in this layer. This troposphere contains almost all the water vapour and most of the dust particles.

• All biological activities take place in this layer.