Short answer: the deepest known point in the ocean is the Challenger Deep, at the southern end of the Mariana Trench in the western Pacific. It sits about 10,935 meters (35,876 feet) below sea level. That is deeper than Mount Everest is tall. Here is where it is, how we know the number, and who has actually been down there.
Where is it?
The Challenger Deep lies beneath the western Pacific Ocean, at the southern end of the Mariana Trench, several hundred kilometers southwest of the U.S. territorial island of Guam (NOAA Ocean Service).
It is named after HMS Challenger, whose crew first sounded the depths of the trench in 1875 (NOAA). Sounding back then meant lowering a weighted line and waiting. A long wait.
The Challenger Deep is not one hole. It is three basins, western, central and eastern, each more than 10,900 meters deep (Greenaway et al., 2021).
How deep, really?
NOAA uses about 10,935 meters (35,876 feet) (NOAA). That figure comes from a 2021 paper in Deep-Sea Research Part I led by NOAA's Samuel Greenaway. In June 2020, Victor Vescovo made multiple dives to the bottom in the crewed submersible Limiting Factor, alongside three instrumented landers, and the team made six transects across the candidate deepest spots. Using pressure-referenced altimeter readings, they found the deepest observed seafloor at 10,935 meters, plus or minus 6 meters, below mean sea level (Greenaway et al., 2021).
Why the fuss over a few meters? Because nobody agreed. The same paper lists modern sonar-based estimates of the maximum depth ranging from about 10,920 to 10,989 meters, and notes that the disagreement between them is bigger than each one's claimed uncertainty. They didn't even agree on which basin held the deepest point (Greenaway et al., 2021). Measuring the bottom of the world from a ship, through 11 kilometers of water with changing temperature and salinity, is hard.
Deeper than Everest is tall
NOAA Fisheries puts it plainly: Challenger Deep is about 7,000 feet deeper than Mount Everest is tall (NOAA Fisheries). Drop the tallest mountain on land into the trench and its summit would still be underwater by more than a mile.
For scale, the average depth of the whole ocean is 3,682 meters (12,080 feet) (NOAA). The Challenger Deep is roughly three times that.
The pressure down there
The 2020 team calibrated their sensors against a reference pressure of about 11,250 decibars, at roughly 10,920 meters (Greenaway et al., 2021). That is more than 1,000 times the air pressure you feel at sea level. Anything going down there needs to be built like a bank vault.
Who has been to the bottom?
Very few machines and fewer people. Before Limiting Factor, the Greenaway paper counts only two crewed submersibles, three uncrewed vehicles and a small number of free-fall landers known to have reached the Challenger Deep (Greenaway et al., 2021):
- 1960: Jacques Piccard and Lt. Don Walsh of the U.S. Navy in the bathyscaph Trieste. It was the first visit, ever (NOAA Ocean Exploration).
- 1995 and 1998: JAMSTEC's remotely operated vehicle Kaiko.
- 2008: JAMSTEC's ROV ABISMO.
- 2009: Woods Hole Oceanographic Institution's hybrid vehicle Nereus.
- 2012: James Cameron, solo, in Deepsea Challenger.
The Trieste depth itself has a messy history. The paper notes a pressure-derived depth of 10,910 meters, from a gauge originally calibrated in fresh water and corrected later (Greenaway et al., 2021). NOAA's own history timeline records 10,915 meters (NOAA Ocean Exploration). Measuring the abyss with 1960 tech was very much a judgment call.
The neighborhood is weird too
The trench sits inside the Mariana Trench Marine National Monument, established by presidential proclamation in January 2009. It covers about 95,216 square miles of submerged lands and waters (NOAA Fisheries). In that same monument, according to NOAA:
- The Champagne vent at NW Eifuku volcano releases almost pure liquid carbon dioxide. It is one of only two known liquid CO2 sites in the world.
- The Daikoku submarine volcano has a pool of liquid sulfur. The only other known molten sulfur is on Jupiter's moon Io.
- Vents pumping out highly acidic, boiling water still support living things.
We still haven't seen most of it
The deepest spot is famous. Most of the seafloor is not. NOAA Ocean Exploration says only about 26 percent of Earth's seafloor had been mapped in high resolution as of June 2024 (NOAA Ocean Exploration). The Nippon Foundation-GEBCO Seabed 2030 project aims for a high-resolution map of the whole seafloor by 2030 (NOAA Ocean Exploration). So the "deepest point" is the deepest point we know of. Keep that in mind.
Sources: NOAA Ocean Service, "How deep is the ocean?" · Greenaway et al. (2021), Deep-Sea Research Part I 178:103644 · NOAA Fisheries, Mariana Trench Marine National Monument · NOAA Ocean Exploration history timeline · NOAA Ocean Exploration, ocean depth