Covering over 70% of the planet, the ocean’s immense depths remain largely unexplored. This vast, mysterious environment has long captivated human curiosity, driving ongoing efforts to uncover its secrets.
The Human Body’s Limits in the Deep
The human body faces severe physiological challenges when exposed to the high pressures and unique gas environments of the deep ocean. As a diver descends, the pressure increases significantly, leading to a compression of air spaces within the body, such as the lungs, sinuses, and middle ears. This pressure can cause barotrauma, or squeeze injuries, if not properly equalized.
At greater depths, the elevated partial pressures of gases like nitrogen and oxygen become problematic. Nitrogen narcosis, sometimes called “rapture of the deep,” occurs when nitrogen dissolves in bodily tissues and affects neurological function, impairing judgment and motor skills. Oxygen, while essential for life, becomes toxic at high partial pressures, potentially causing convulsions and central nervous system damage.
Decompression sickness, commonly known as “the bends,” is a serious concern. It arises when dissolved gases, primarily nitrogen, form bubbles in the blood and tissues if a diver ascends too quickly. These bubbles can obstruct blood flow and cause pain, joint damage, paralysis, or even death. Managing these physiological responses requires specialized training, equipment, and strict adherence to decompression protocols.
Reaching Depths Without Submersibles
Humans have pushed the boundaries of unassisted and minimally-assisted diving through breath-hold (free diving) and scuba diving. Free divers, relying solely on their lung capacity and physiological adaptations, can achieve remarkable depths. The current world record for constant weight free diving, where the diver descends and ascends using only fins and no changes in ballast, is around 130 meters (426 feet).
Scuba diving, which uses self-contained underwater breathing apparatus, allows for longer durations underwater but is still limited by pressure and gas absorption. The deepest scuba dive ever recorded, using specialized gas mixtures to mitigate narcosis and oxygen toxicity, reached 332 meters (1,089 feet) in 2014. Beyond these depths, the risks from decompression sickness and gas toxicities increase dramatically, making further descent without protective vehicles impractical.
Exploring the Abyss in Submersibles
To venture into the ocean’s most extreme depths, humans rely on advanced submersibles and bathyscaphes. These specialized vehicles are engineered to withstand immense pressures, which can exceed 1,000 times atmospheric pressure at the surface. Their robust pressure hulls, often spherical, protect the occupants and maintain a habitable internal environment.
The deepest point ever reached by a crewed submersible is the Challenger Deep, located in the Mariana Trench. In 1960, the bathyscaphe Trieste, carrying Jacques Piccard and Don Walsh, descended to approximately 10,911 meters (35,797 feet). More recently, in 2012, filmmaker James Cameron made a solo dive to 10,908 meters (35,787 feet) in his submersible, the Deepsea Challenger.
The Ocean’s Deepest Points
The deepest known part of the global ocean is the Challenger Deep, situated in the southern end of the Mariana Trench in the western Pacific Ocean. This profound depression plunges to approximately 10,935 meters (35,876 feet) below the surface. The Mariana Trench itself is a crescent-shaped geological feature stretching about 2,550 kilometers (1,580 miles) long and 69 kilometers (43 miles) wide.
Other significant deep points include the Tonga Trench and the Philippine Trench in the Pacific, and the Puerto Rico Trench in the Atlantic. These trenches are formed by the process of tectonic plate subduction, where one oceanic plate slides beneath another. The conditions in these hadal zones, depths greater than 6,000 meters, are characterized by perpetual darkness, near-freezing temperatures, and immense pressure.