Approximately 71% of the Earth's surface corresponds to the oceans. As well as the continental portions (emerged lands), the bottom of the oceans also presents irregularities in its composition, being classified as underwater relief.
The average depth of the oceans is 3,800 meters. On continental shelves, where the depth is less, the variation is from 0 to 180 meters. On the other hand, ocean trenches have the greatest depths of the underwater relief, where the average is 6,000 meters.
Ocean trenches are large depressions that formed as a result of the convergent movements of tectonic plates (encounter of different plates). In these regions there is a high atmospheric pressure, few plants, total absence of light and low temperatures.
These characteristics hinder the development and presence of marine species. Heterotrophic bacteria, sponges, sea anemones, blind fish and scavengers (species that feed on organic debris) are the only inhabitants of ocean trenches.
At 11,516 meters deep, the Mariana Trench, located in the Pacific Ocean, is the deepest ocean trench. Other trenches of great prominence are: Kermadec Trench (10,047 meters), Puerto Rico Trench (8,648 meters), Java Trench (7,725 meters) and South Sandwich Trench (7,235 meters).
By Wagner de Cerqueira and Francisco
Graduated in Geography
Source: Brazil School - https://brasilescola.uol.com.br/geografia/fossa-oceanica.htm