The average height of the continents above sea level is about 850m and the average depth of the ocean is about 3800m. The Pacific Ocean covers most of the ocean area & is larger than all of the continents put together. Most of the ocean's area lies in the Southern Hemisphere, 80% water & 20% land, while the Northern Hemisphere is about 60% water & 40% land. Some of the world's largest oceans didn't exist 200 million years ago, with the Atlantic, Indian & Southern Oceans beginning as cracks in the continental crust. The cracks slowly widened as new molten rock formed new basalt rock in the spaces in between. Ocean water then flooded in over this basalt. New oceanic crust kept on forming. Molten basalt rocks rose & broke through the sea floors along the crests of mid-ocean ridges marking the original cracks in the crust. This forced the sea floors on either side further apart widening the oceans. This process keeps repeating itself, the sea floor spreads at a rate of about 6cm per year on both sides of the mid-ocean ridges.

The ocean floor consists of relatively thin & heavy igneous basalt-type rocks, formed from a molten state during the last 200 million years, which is considered quite young. This consistently moves sideways by currents beneath the crust, allowing new molten rock to rise & form new areas of ocean floor, causing older areas to sink into the Earth's interior.

The Oceans contain the smallest micro-organisms to the planets largest creatures. It can also provide the world with a long term source of food and income if fisheries are managed sustainably. This would entail turning away from large scale industrial exploitation and also enforcing the United Nations moratorium on drift nets. Governments, regional maritime organizations and fishermen are being pressured to think of the seas, not as a quick cash, but as a global resource that must be preserved.

Over the years, high seas driftnets have killed millions of birds, turtles, dolphins, whales and seals. Even though the moratorium on drift nets has been adopted, destructive fishing practices continue to jeopardize the world's fisheries. Huge hitech factory trawlers routinely ply the seas, hauling in up to 350 000 pounds of fish in a single catch. Unwanted fish are dumped back into the ocean - dead. These wasteful commercial fishing practices have resulted in spectacular declines in fish stocks around the world.

Most of the wastes we dump into the air, water and land eventually end up in the oceans. Oil slicks, floating debris, polluted estuaries and beaches contaminate fish and shellfish, visible signs that we are using the oceans as the worlds largest trash dump.

The ocean covers more than 70% of the Earth's surface and play a key role in the survival of virtually all life.