Final answer:
The Challenger Deep was discovered using high-resolution sonar mapping from research vessels, which is a technique that measures the time for sound waves to bounce back from the ocean floor.
Step-by-step explanation:
The deepest part of Challenger Deep was discovered through the utilization of high-resolution sonar mapping from research vessels. Before the advent of advanced technology, sailors would measure ocean depth using a fathom line—a rope knotted every six feet.
Today, scientists use sonar, which stands for Sound Navigation And Ranging, to map out underwater terrain. Sonar works by emitting sound waves that travel to the ocean floor and bounce back to the surface. By calculating the time it takes for the sound waves to return and knowing the speed of sound in water, researchers can determine the depth with great precision. This method is one of the primary ways through which previously uncharted areas like the Challenger Deep are explored and mapped.