The Earth is often called the ‘blue planet’ or ‘Watery Planet’. This is because three-fourths of the Earth’s is covered with water and this gives it a distinct blue color when seen from outer space. All the water bodies together from the Hydrosphere, major part of which is contained in the large oceans. The southern Hemisphere, which has more oceans than land area, is often referred to as the water hemisphere. Ocean waters contain roughly 97 per cent of all the Earth’s water. The remaining 3 percent is fresh water, found in rivers and lakes in the form of snow or ice, underground water and as water in the atmosphere. The amount of water on Earth remains constant. There is a continuous cycle of evaporation and condensation starting from the sea and finishing in the sea. This is called Water Cycle. Due to the heat of the sun, the water in oceans, lakes and rivers evaporates. Water from moist soil, trees and from living things is constantly evaporating. The heat of the sun warms up the air near the ground surface. This warm air containing the water vapor is lighter and hence rises up. And as the temperature of the atmosphere decreases with altitude, the warm air cools (condenses) at higher altitudes. On condensation, water vapor turns into water droplets which from clouds. These droplets come closer and combine to from drops of water, which fall as rain. The rainwater finally goes back to sea again. This is how the water cycle is completed.