Do you know that about three-fourths of the Earth’s surface is covered with water? There are three main oceans — the Atlantic, the Pacific and the Indian Ocean. The Arctic Ocean is taken to be a part of the Atlantic Ocean, and the Antarctic Ocean is made up of the southern part and other oceans. The Atlantic Ocean is a great mass of water that separates Europe and Africa, from the American continent. It is shaped like an hourglass, with a ‘waist’ where Africa and South America bulge out towards each other. Although in area it is less than half of the Pacific Ocean, it has many ‘secondary’ water bodies, such as the Arctic Ocean and the Mediterranean sea. The Mediterranean Sea lies between Southern Europe, Africa and South-West Asia. It is linked to the Atlantic Ocean through the narrow strait of Gibraltar in the west and to the Black Sea in the north-east by the sea of Marmara. One of the surprising facts about the Mediterranean Sea and the Atlantic Ocean is that while the water of the former appears blue, that of the latter appears green! Can you guess why this happens? The varying colours of the Mediterranean Sea and the Atlantic Ocean depend mainly on the amount of sunlight scattered from their surface. The colour of the scattered sunlight depends upon the substances dissolved in seawater. Generally, of the seven colours of the sunlight, blue is scattered most. That is why most oceans appear blue. However, in the case of the Atlantic Ocean, the green effect is produced by the decaying plants in the ocean bed. When these plants decay, yellow pigments are released which get dissolved in the water. The water now scatters both blue and yellow light, and the resulting mixture produces the characteristic green shade.