Measuring the Greatest Ocean Depth

The Challenger Deep in the Mariana Trench is the deepest known point in Earth's oceans. In 2010 the United States Center for Coastal & Ocean Mapping measured the depth of the Challenger Deep at 10,994 meters (36,070 feet) below sea level with an estimated vertical accuracy of ± 40 meters. If Mount Everest, the highest mountain on Earth, were placed at this location it would be covered by over one mile of water. 

The first depth measurements in the Mariana Trench were made by the British survey ship HMS Challenger, which was used by the Royal Navy in 1875 to conduct research in the trench. The greatest depth that they recorded at that time was 8,184 meters (26,850 feet). 

In 1951, another Royal Navy vessel, also named the "HMS Challenger", returned to the area for additional measurements. They discovered an even deeper location with a depth of 10,900 meters (35,760 feet) determined by echo sounding. The Challenger Deep was named after the Royal Navy vessel.

In 2009, sonar mapping done by researchers aboard the RV Kilo Moana, operated by the University of Hawaii, determined the depth to be 10,971 meters (35,994 feet) with a potential error of ± 22 meters. The most recent measurement is the 10,994 meter ( ± 40 meter accuracy) depth reported above by the United States Center for Coastal & Ocean Mapping.