The world’s oceans cover two-thirds of the Earth’s surface.
The seabed, or ocean floor, is the bottom of the ocean. The ocean floor has four different levels.
They are the continental shelf, continental slope, trench and seamount.
Parts of the ocean floor
• Continental Shelf – the edge of a continent that extends under water.
• Continental Slope – the end of a continent
• Trench – a deep, narrow valley in the sea floor
• Seamount – a cone-shaped under water mountain formed by a volcano
What are the highest and lowest places on Earth? If you named Mt Everest and the Grand Canyon, you are incorrect! The tallest mountains and deepest canyons are actually found in the ocean. If placed side by side, the Hawaiian Islands of the Pacific Ocean would tower over Mt Everest. The Pacific is also home to the deepest trench on the Earth, the Mariana Trench. It measures 11 kilometres below the sea’s surface. This is seven times the depth of the Grand Canyon.
Exploring the ocean
People have explored the oceans for thousands of years. Until recently, however, the ocean floor has not been studied and much
was unknown about the
deep oceans. Why is this? Studying the ocean floor is difficult; conditions are very harsh in the deep ocean. The ocean floor seems like a different world. There is no sunlight down there, as sunlight does not penetrate far below the surface. The water is very cold, only a few degrees above freezing, and the pressure of the weight of kilometres of water above this area would easily crush a submarine. Tiny flecks of material from the sunlit world float downwards and eventually settle on the bottom. There is almost nothing to eat, and the fish that live here are few and far between and are able to survive on very little.
Because of the darkness, cold, and extreme pressure, scientists have had to develop technology to enable them to study the deep ocean floor. That technology includes sonar, scuba, submersibles, satellites, remote underwater manipulators, and gravity mapping. The development of sonar was a major breakthrough for mapping the ocean floor. Sonar, which stands for sound navigation and ranging, is a system that uses sound waves to calculate the distance to an object. The sonar equipment on a ship sends out pulses of sound that bounce off the ocean floor. The equipment then measures how quickly the sound waves return to the ship. Sound waves return quickly if the ocean floor is close but take longer to return if the ocean floor is further away. Using sonar, scientists were able to
develop detailed maps of the ocean floor.
Features of the ocean floor
Once scientists were able to map the ocean floor, they discovered something surprising. The bottom of the ocean was not a flat, sandy plain stretching between the continents, as many people once thought. In fact, it was rocky and dramatically uneven. Thanks to Alvin (below), a 16-ton, manned deep-ocean research submarine, the seabed can now be explored in more detail.