<P> It has been suggested that more is known about the Moon than the deepest parts of the ocean . Little was known about the extent of life on the deep ocean floor until the discovery of thriving colonies of shrimps and other organisms around hydrothermal vents in the late 1970s . Before the discovery of the undersea vents, it had been accepted that almost all life on earth obtained its energy (one way or another) from the sun . The new discoveries revealed groups of creatures that obtained nutrients and energy directly from thermal sources and chemical reactions associated with changes to mineral deposits . These organisms thrive in completely lightless and anaerobic environments in highly saline water that may reach 300 ° F (150 ° C), drawing their sustenance from hydrogen sulfide, which is highly toxic to almost all terrestrial life . The revolutionary discovery that life can exist under these extreme conditions changed opinions about the chances of there being life elsewhere in the universe . Scientists now speculate that Europa, one of Jupiter's moons, may be able to support life beneath its icy surface, where there is evidence of a global ocean of liquid water . </P> <P> Natural light does not penetrate the deep ocean, with the exception of the upper parts of the mesopelagic . Since photosynthesis is not possible, plants cannot live in this zone . Since plants are the primary producers of almost all of earth's ecosystems, life in this area of the ocean must depend on energy sources from elsewhere . Except for the areas close to the hydrothermal vents, this energy comes from organic material drifting down from the photic zone . The sinking organic material is composed of algal particulates, detritus, and other forms of biological waste, which is collectively referred to as marine snow . </P> <P> Because pressure in the ocean increases by about 1 atmosphere for every 10 meters of depth, the amount of pressure experienced by many marine organisms is extreme . Until recent years, the scientific community lacked detailed information about the effects of pressure on most deep sea organisms because the specimens encountered arrived at the surface dead or dying and weren't observable at the pressures at which they lived . With the advent of traps that incorporate a special pressure - maintaining chamber, undamaged larger metazoan animals have been retrieved from the deep sea in good condition . </P> <P> Salinity is remarkably constant throughout the deep sea, at about 35 parts per thousand . There are some minor differences in salinity, but none that is ecologically significant, except in the Mediterranean and Red Seas . </P>

In which of the following ocean zone(s) is there no light