Oceans lay claim to about 70 percent of the surface of the earth, and ocean life accounts for 94 percent of living things. Despite this, scientists have yet to explore most of the ocean, as its average depth surpasses 12,400 feet and is mostly cloaked in darkness.
Many of the earth's most dramatic landforms exist under the ocean. The Pacific Ocean is home to the Mariana Trench, which at its lowest level of 36,000 feet below the surface of the sea is the planet's lowest known point. The earth's largest mountain range, the Mid-Oceanic Ridge, runs more than 35,000 miles through parts of the Atlantic, Pacific and Indian Oceans. Additional geographic features include pillars, underwater volcanoes and hot springs.
Creatures living in the ocean adapt to their environment in several ways. Crabs and tubeworms are able to survive at depths that would crush humans and large ships. Many species of octopuses can change their colors in order to blend in to the surrounding environment. Long jellies live on hot hydrothermal vents and utilize a process known as chemosynthesis to manufacture their own food, as the lack of sunlight prevents normal photosynthesis from occurring. This happens even though vent temperatures can reach 390 degrees Fahrenheit.