Good question! The average depth of the ocean is about 14,000 feet (2.65 miles; NOAA.gov). The deepest part of the ocean is in the Mariana Trench in the west Pacific Ocean. This location, known as the Challenger Deep, is about 36,200 feet deep (NOAA.gov). That is so deep, that if Mount Everest were sitting on the seafloor in the Challenger Deep, the top would still be under water! I don’t know how long the average person can hold their breath under water… According to Wikipedia, the record for the longest time that a person has held their breath under water is 22 minutes breath under water !

Of the animals that need to breathe oxygen gas (as opposed to fish and other aquatic organisms that obtain oxygen that’s dissolved in water), the sperm whale holds the record for holding its breath the longest. Sperm whales can hold there breath for up to 2 hours, while diving more than 6,000 feet deep (Watkins et al., 2002, Marine Mammal Science)! Some types of turtles are able to stay submerged for even longer, but perhaps this shouldn’t count. Turtles get most of their oxygen from breathing air, but they can also absorb oxygen that is dissolved in water. Musk turtles have been observed to survive for seven months underwater by absorbing oxygen through their skin (Belkin, 1968, Respiration Physiology).