What is the deepest known point in Earth's seabed?

The deepest known point in Earth's seabed is Challenger Deep.

Challenger Deep is a depression at the southern end of the Mariana Trench in the western Pacific Ocean, within the waters of the Federated States of Micronesia. Modern measurements place its deepest areas at roughly 10,900 to 11,000 meters below sea level, although the exact figure varies with survey methods and the location of the sounding.

The feature was first detected during the 1872–1876 voyage of HMS Challenger, one of the first major oceanographic expeditions. It takes its name from that ship and from HMS Challenger II, whose 1950–1952 survey confirmed the extraordinary depth. In January 1960, Jacques Piccard and U.S. Navy officer Don Walsh became the first people to reach the bottom in the bathyscaphe Trieste.

A common mistake is treating the Mariana Trench and Challenger Deep as interchangeable. The Mariana Trench is the much larger geological trench; Challenger Deep is its deepest known point. Other deep sites, including Sirena Deep, are impressive but do not currently exceed Challenger Deep in measured depth.