The Mariana Trench is a deep canyon in the ocean floor, about halfway between Japan and Australia. Only about 10 people have ever made it to the bottom.
Vescovo and Sullivan had descended deep into the ocean’s waters to help map the ocean floor. “We know more about the moon and Mars than we do about the deep sea,” Sullivan points out.
Why is exploring the Mariana Trench so difficult? That question can be answered in just one word: pressure. At the bottom of the ocean, 7 miles’ worth of water presses down on you.
A normal sub would crack under the strain, but Vescovo had his sub built to handle it. The walls—made of an extremely strong metal—are 3.5 inches thick.
So, during the four-hour trip down, both divers were able to relax. They even snacked on tuna fish sandwiches! “Lunch at 31,000 feet below sea level,” Sullivan says. “Doesn’t everybody do that?”