Marine biology is the scientific study of the biology of marine life, organisms in the sea. A large proportion of all life on Earth lives in the ocean. The exact size of this large proportion is unknown, since many ocean species are still to be discovered. The ocean is a complex three-dimensional world covering approximately 71% of the Earth's surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the oceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean.
Thumbnail: Ocean sunfish -Mola mola (C BY-SA 2.5 Generic; OpenCage via Wikipedia)