Unit 3 Under the seaThe earth's oceans can reach depths of up to 11,000 metres. That is deep enough to cover Mt. Qomolangma! The oceans are incredibly (不能相信地) large and contain several different habitats. To make it easier to describe the various parts of the oceans, marine (海洋的) scientists usually divide the oceans into five zones. Each zone is different mainly as a result of how much sunlight reaches it.Most of the life in the ocean can be found in the first zone, which begins at the surface and goes down about 200 metres. Because there is sunlight at this level, plants are able to grow. Marine animals such as dolphins, sharks, sea turtles and sea lions, and of course a variety of fish, live in the sunlit (阳光照射的) part of the ocean. It is difficult to hide from other animals in this area.The second zone starts at 200 metres and goes down to about 1,000 metres. Some sunlight can reach this level, but it is not enough for plants to grow. Because this zone is relatively dark, many of the creatures that live here are able to make light with their body. The light from these animals makes the water look like a sky with moving stars in it.The third zone of the ocean is dark. This place, about 3,000 metres deep, may not seem a likely habitat, but there are more creatures here than one might think. Most of the animals that live here are black or red because of the lack of light.Below 4,000 metres, the temperature is near freezing and there is no light at all. In fact, the zone is so dark and empty that scientists named this zone after the Greek word for “no bottom”. There is not much life to be found in this cold and unpleasant part of the ocean, but so...
