The mapping of the seafloor has altered since the invention of sonar. A transducer, a device that combines a transmitter and a receiver, emits a sound pulse directly into the water. The vibration reflects off the ocean floor as it travels through the water and descends. The transducer can hear the reflected sound. The time it takes for the sound pulse to travel to the bottom and back is precisely measured by computers. Sound waves bounce back fairly quickly in shallow water, whereas it takes longer to hear the echoes in deeper water. When you know how fast sound travels through water, you can compute the ocean’s depth (approximately 1,500 meters per second).