Hint: The atmosphere is a blanket of gases that surrounds the earth. It is kept close to the planet's surface by the earth's magnetic field. It is very essential for life on earth.
Complete Answer: The atmosphere contains the air that we breathe; protects us from the harmful radiation of the Sun; helps to keep the planet's heat on the surface, and plays a very important role in the water cycle. The atmosphere is made up of a combination of gases, especially nitrogen, oxygen, argon, and carbon dioxide, reaching more than 500km above the planet's surface. Plants require carbon dioxide for photosynthesis; they use sunlight to change carbon dioxide and water into food. Also, without photosynthesis, there would be very little oxygen in the air. Plants release oxygen to get energy from food, even plants need oxygen for this purpose. Sound waves cannot travel through empty space, but they can travel through the atmosphere. Without the atmosphere there would be no sound. The atmosphere continues to decline in thickness sharply, until it finally reaches and dissolves in space. The atmosphere is divided into layers. They are Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
Note: Wherever there is atmosphere, there is air pressure. Atmospheric pressure is the pressure exerted on the surface of the earth by the weight of air. Atmospheric pressure is measured with a barometer. The denser the air molecules, the higher the pressure. Air pressure is affected by altitude, moisture, and temperature.