1. How did people 1st map the ocean floor?

Echo sounding is the key method scientists use to map the seafloor today. The technique, first used by German scientists in the early 20th century, uses sound waves bounced off the ocean bottom ... The time taken for the sound to travel through the ocean and back is then used to calculate water depths.

used sound waves that bounced off the ocean bottom. the time taken for the sound to travel through the ocean and back is then used to calculate water depths