The earth is a vast planet. It is in shape. One third of its total area is land while the other three portions are covered with . The water areas are divided into oceans, seas and . The surface of the land area is of variety. There are high hills, green forests stretches of deserts. The land mass is divided some continents under each continent, there are a of countries. The interior of the earth is in mineral resources. There is existence of life only on earth. But, this existence of life would be impossible sunlight. In fact, sunlight is the prerequisite for the existence of all types of living beings.