What do you understand by atmosphere?
The atmosphere is a mixture of different gases that envelopes the earth all round. It contains life-giving gases like oxygen for humans and animals and carbon dioxide for plants. The atmosphere is composed of gases, water vapour and dust particles.
The air is an integral part of the earth's mass and 99 per cent of the total mass of the atmosphere is confined to the height of 32 km from the earth's surface. The air is colourless and odourless and can be felt only when it blows as wind.
The atmosphere consists of different layers with varying density and temperature. Density is highest near the surface of the earth and decreases with increasing altitude. The column of atmosphere is divided into five layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere.
Explanation
This question tests the student's understanding of the basic concept of atmosphere. The textbook defines atmosphere as a mixture of gases enveloping the earth, containing life-giving gases. Key points include its composition (gases, water vapour, dust), its mass distribution (99% within 32 km), and its layered structure with varying density and temperature.