Enormous Water Pressure
The water pressures at such depths are incredible. At the bottom of the Mariana Trench, the 11 kilometers (7 miles) of overlying water exert a pressure of more than 1,100 kilograms per square centimeter (16,000 pounds per square inch). At that pressure, an unprotected human being would be crushed to death. And yet, even in such a hostile environment there is life, including a primitive type of shrimp.
At lesser depths of the deep ocean, marine biologists have found hundreds of life forms, ranging from single-celled microorganisms to crabs, worms, and fish. There are no plants because there is no light to support photosynthesis, the process by which plants use the energy of sunlight to grow. Most of the food that sustains life at the bottom is organic debris that drifts down from the waters nearer the surface. Also, hydrothermal vents and cold seeps (areas where methane escapes from deeply buried deposits) support dense populations of specialized bacteria that live by chemosynthesis–the manufacture of nutrients from hydrogen sulfide or methane. Animals that live near the vents feed on these bacteria and on each other.