The deepest place on Earth is the Challenger Deep, sitting approximately 10,935 meters (35,876 feet) below the surface of the western Pacific Ocean. But every ocean has its own deepest point, and a 2019 expedition mapped all five with modern precision for the first time. Here’s where the ocean floor bottoms out in each basin and what conditions are like at those extremes.
Challenger Deep: The Deepest Place on Earth
The Challenger Deep lies at the southern end of the Mariana Trench, a crescent-shaped scar in the seafloor that runs several hundred kilometers southwest of Guam. At roughly 10,935 meters deep, it’s more than 2 kilometers deeper than Mount Everest is tall. If you dropped Everest into the Mariana Trench, its summit would still sit under more than a mile of water.
The trench exists because the Pacific tectonic plate is diving beneath the smaller Mariana plate, a process called subduction. This collision zone has been pulling the seafloor downward for millions of years, creating the deepest groove on the planet’s surface.
The Deepest Points in All Five Oceans
The Five Deeps Expedition, led by explorer Victor Vescovo in 2019, set out to visit and precisely map the lowest point in every ocean. Using high-resolution sonar, the team confirmed or corrected previous depth estimates across the globe. Here’s what they found:
- Pacific Ocean: Challenger Deep, Mariana Trench, at 10,935 meters (35,876 feet). By far the deepest spot on Earth.
- Atlantic Ocean: Brownson Deep, Puerto Rico Trench, at 8,378 meters (27,487 feet). Located north of Puerto Rico in the Caribbean region.
- Southern Ocean: Factorian Deep, South Sandwich Trench, at 7,432 meters (24,383 feet). This was a new discovery, not previously recognized as the Southern Ocean’s deepest point.
- Indian Ocean: An unnamed point in the Java Trench, at 7,187 meters (23,579 feet). The Java Trench stretches more than 4,000 kilometers along the coast of Indonesia. Before the expedition, scientists thought the deepest section was 387 kilometers away from where it actually turned out to be.
- Arctic Ocean: Molloy Hole, at 5,551 meters (18,212 feet). Located in the Fram Strait between Greenland and Svalbard, it’s the shallowest of the five deepest points but still deeper than most of the world’s ocean floor.
The gap between the Pacific and everything else is striking. Challenger Deep is more than 2,500 meters deeper than the Atlantic’s lowest point, and nearly double the depth of the Arctic’s. The Pacific Ocean sits on the most tectonically active boundaries on Earth, which explains why it produces the most extreme depths.
What Conditions Are Like at the Bottom
At the bottom of the Mariana Trench, the water column above exerts 1,086 bars of pressure, equivalent to about 15,750 pounds per square inch. For perspective, that’s roughly 1,000 times the atmospheric pressure you feel standing at sea level. Any vessel visiting these depths needs walls thick enough to resist forces that would instantly crush most submarines.
Temperature at the bottom of deep trenches hovers just above freezing, remarkably uniform throughout the deepest waters. Measurements from Pacific trenches show water temperature varies by only hundredths of a degree across the entire hadal zone (the layer below 6,000 meters). There is dissolved oxygen at these depths, though slightly less than in the water above the trench rim. Geothermal heat seeping up from the Earth’s interior warms the trapped water by a tiny but measurable amount, and biological activity inside the trench consumes some of the available oxygen.
Despite these crushing, cold, dark conditions, life exists at the bottom. Researchers have found microbial communities, shrimp-like amphipods, and even fish adapted to hadal pressures. The biological activity is significant enough to alter the water chemistry inside the trenches compared to the open ocean at similar depths.
How These Depths Are Measured
Modern ocean depth measurements rely on multibeam sonar systems mounted on ship hulls. These instruments send out fans of sound pulses toward the seafloor and calculate depth based on how long the echoes take to return. The tricky part is that sound travels at different speeds depending on water temperature, salinity, and pressure, all of which change as depth increases. To get accurate readings, researchers continuously measure the speed of sound at the ship and feed detailed sound speed profiles into the sonar system to correct for these variations.
Before this technology, depth estimates came from single-beam soundings or weighted lines dropped over the side of a ship. Early measurements of the Challenger Deep in the 1870s used rope and a heavy weight, a method accurate to within a few hundred meters at best. The Five Deeps Expedition’s multibeam surveys corrected longstanding errors in several oceans, shifting the known locations of deepest points by hundreds of kilometers in some cases. The Indian Ocean’s deepest spot moved 387 kilometers from where older charts had placed it.
Why Some Oceans Are Deeper Than Others
Ocean depth is controlled by plate tectonics. The deepest trenches form at subduction zones, where one tectonic plate slides beneath another and pulls the seafloor downward. The Pacific Ocean is surrounded by subduction zones (the so-called Ring of Fire), giving it the most and deepest trenches. The Atlantic has fewer subduction boundaries, which is why its deepest point is more than 2,500 meters shallower than the Pacific’s.
The Arctic Ocean is the shallowest of the five because it’s largely enclosed by continental landmasses, with a broad, shallow continental shelf covering much of its floor. The Molloy Hole is a small, isolated depression rather than a long trench, formed by tectonic spreading rather than subduction. The Southern Ocean’s South Sandwich Trench, by contrast, sits along a proper subduction zone where the South American plate dives beneath the small South Sandwich plate, which is why it reaches depths competitive with the Indian Ocean despite surrounding one of the least-explored regions on Earth.