Deep Sea Exploration

For centuries, the deep ocean remained difficult to explore because sunlight disappears rapidly with depth, pressure increases enormously, and the water is cold. The deepest parts, known as the hadal zone, lie below about 6,000 metres, while the abyssal zone generally extends from about 3,000 to 6,000 metres. Scientific exploration began to advance in the 19th century.

Between 1872 and 1876, the HMS Challenger expedition made thousands of measurements across the oceans and collected specimens from deep water and the seafloor. Its results revealed a rich variety of marine life and provided important information about ocean depth, temperature, and sediments. Even so, most of the deep seafloor remained beyond direct human observation.

New technology changed this situation during the 20th century. In 1934, William Beebe and Otis Barton descended in the bathysphere to about 923 metres, allowing Beebe to observe deep-sea animals in their natural environment. In 1960, Jacques Piccard and Don Walsh reached the Challenger Deep in the Mariana Trench aboard the bathyscaphe Trieste, descending to nearly 11,000 metres.

Later, remotely operated vehicles and crewed submersibles made repeated dives possible and greatly expanded research. In 1977, scientists using the submersible Alvin discovered hydrothermal vents near the Galápagos Islands, where ecosystems exist without sunlight and rely on chemical energy. Today, deep-sea exploration continues to study biodiversity, geology, ocean chemistry, and climate, while revealing how much of the seafloor still remains insufficiently known.