Answer:
Sounding
Step-by-step explanation:
The crew of the HMS Challenger used a process called sounding to measure the depths of the ocean floor. Sounding is a technique in which a weighted line is lowered into the water, and the depth is measured by determining the length of line that is needed to reach the bottom of the ocean. This process was used extensively by the crew of the HMS Challenger during their voyage, and they recorded thousands of soundings in order to map the depths and contours of the ocean floor.