What is the Mariana Trench?
The Mariana Trench is a long, narrow valley or canyon on the ocean floor in the western Pacific Ocean. It was formed where two massive pieces of Earth's crust, called tectonic plates, meet and one plate slides beneath the other in a process called subduction. This trench is not just the deepest point in the ocean, but the deepest location on Earth.
Challenger Deep
Challenger Deep is the specific location within the Mariana Trench where the ocean reaches its greatest depth. The name comes from the HMS Challenger, a research ship that first measured the trench's depth in 1875. In recent years, advanced technology has allowed scientists to measure this location more accurately at 36,070 feet deep, making it nearly 7 miles below the ocean's surface.
Extreme Conditions at the Deepest Ocean
The environment at Challenger Deep is extremely harsh. The water pressure is over 1,000 times greater than the pressure at sea level. The temperature is close to freezing, and almost no sunlight reaches this depth. Despite these extreme conditions, scientists have discovered that life exists even here, including small fish, shrimp, and microorganisms specially adapted to survive in this environment.
Human Exploration
Very few people have visited the deepest part of the ocean. In 1960, Jacques Piccard and Don Walsh reached Challenger Deep in a special submersible called the Trieste. More recently, filmmaker James Cameron descended to the trench in 2012 in a specially designed submarine, making observations and collecting samples for scientific study.
How Depth is Measured
Ocean depth is measured using sonar technology, which sends sound waves down to the ocean floor and measures how long it takes for the sound to return. Modern satellite and underwater mapping systems have provided increasingly accurate measurements of ocean depths. Scientists continue to refine these measurements using advanced equipment and exploration vessels. 
Answer