What are the environmental conditions and the living conditions of the deep ocean?

This would seem to be a simple question to answer, but in some ways we know more about the surface of the moon than we do about the deepest parts of the world's oceans. The water pressure is extreme--as much as 1,100 atmospheres--in the lowest parts of the ocean, which makes it very difficult to collect samples, or even to make observations. Living organisms at that depth not only have had to evolve tissues that...

This would seem to be a simple question to answer, but in some ways we know more about the surface of the moon than we do about the deepest parts of the world's oceans. The water pressure is extreme--as much as 1,100 atmospheres--in the lowest parts of the ocean, which makes it very difficult to collect samples, or even to make observations. Living organisms at that depth not only have had to evolve tissues that survive at that depth, but to utilize alternate methods of obtaining energy. Sunlight can only penetrate to a depth of about 200 meters, meaning that photosynthesis is not possible for the great majority of the oceans' volume. Some organisms are able to utilize energy from thermal vents at the bottom of the oceans; these are known as chemotrophic organisms. Except in the area of the vents, the water temperature is quite cold--about the freezing point of fresh water (0 degrees C.). The water has a lower freezing point, however, because it is salt water. The low temperature also allows for dissolved oxygen sufficient for animal life, which does exist at great depths. The ocean floor is in general covered in sediment or mud. For much more information see the attached link.