The cliffs of Harwick Head in the Orkney Islands are home to many seabirds

Did you know that?

• In some places the ocean is deeper than Mount Everest is high; for example, the Mariana Trench and the Tonga Trench in the western part of the Pacific Ocean reach depths in excess of 10,000 metres (32,800 feet).
• If all the land in the world was flattened out, the Earth would be a smooth sphere completely covered by a continuous layer of seawater 2,686 metres deep.
• Ocean water and ice make up almost 98 percent of all the water on Earth.
• Icebergs are formed by the calving (detaching of parts) of glaciers or of inland ice that reaches the sea. The valley glaciers of Greenland produce some 12,000 to 15,000 sizable icebergs every year.
• The Pacific Ocean is the largest ocean, containing more than twice the volume of water as the Atlantic Ocean.
• Earth is the only planet in our solar system to have oceans.
• Marine fisheries throughout the world catch over 80 million tonnes of fish every year.
• Hundreds of millions of tonnes of toxic chemicals, sewage, industrial waste, agricultural run-off and oil are dumped in the oceans every year – and up to 80 per cent originate on land.
• Each year 20 million tonnes of fish, seabirds, marine mammals and other ocean life are killed unnecessarily by indiscriminate fishing practices.
• Hydrothermal vents, fractures in the sea floor that discharge hot seawater laden with hydrogen sulphide, support the only ecosystem known to run on chemical energy rather than energy from the sun, including mussels, large bivalve clams, and huge tube worms.
• The deepest known point in the ocean is the Mariana Trench which reaches depths of over 36,000 feet (11,000 meters).

After reading these pages try the oceans quiz.

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Photo: M Stecuik/WWF UK