English PSSSB Practice 22

The atmosphere is a vast envelope of gases surrounding the Earth and it is divided into different layers on the basis of temperature, composition, and physical properties. Each layer plays a crucial role in maintaining life and regulating climatic conditions. The Troposphere is the lowest layer, extending up to about 8 km at the poles and nearly 18 km at the equator. It contains almost all the water vapor, clouds, dust particles, and is the region where weather phenomena such as rainfall, storms, and winds occur. Above it lies the Stratosphere, which extends up to about 50 km. This layer is free from weather disturbances and is rich in the ozone layer, which absorbs harmful ultraviolet radiation from the Sun, protecting living beings on Earth. The next layer is the Mesosphere, which stretches from 50 km to nearly 80 km. It is the coldest layer of the atmosphere and is important because most meteors entering the Earth's atmosphere burn up here due to friction. Above it is the Thermosphere, extending from 80 km to about 400 km. This layer contains a high concentration of ions and free electrons and is therefore also known as the ionosphere. It plays a vital role in radio communication by reflecting radio waves back to the Earth. The thermosphere also experiences very high temperatures due to the absorption of solar radiation. The upper part of this layer, the Exosphere, gradually merges with outer space. It extends from around 400 km to 10,000 km and beyond. The exosphere is extremely thin and contains lighter gases such as hydrogen and helium. Artificial satellites and some spacecraft orbit within this region. Together, these layers form a protective shield around the planet, maintaining a balance between incoming and outgoing radiation, preventing extreme temperature fluctuations, and making Earth habitable. Without the layered structure of the atmosphere, life on Earth could not exist in its present form.