Diving today is not just considered a hobby—although, it can be cool to explore the ocean from a fish's perspective—it is also used for tons of other stuff, such as collecting environmental samples, researching marine life, and repairing oil spills. In other words, sometimes diving is work.

We've studied how water pressure increases with depth. How do divers deal with this enormous weight of water?

Divers have to bring along air to breathe under water to reach these huge depths, so they carry on their back tanks of breathing gas. Contrarily to our instincts, this breathing gas does not contain the two most common elements in our atmosphere. Both oxygen and nitrogen actually become poisonous when put under a high enough pressure, and pressure increases with depth. Dun, dun, dun….

Breathing gases are therefore designed based on how deep a diving expedition intends to go. As it happens, the heavy gas argon is commonly used even though it only makes up about 1% of the air in the atmosphere.

We've talked about how gas can exist at different pressures. A diver can withstand huge amounts of pressure because he breathes gas with a pressure that increases with depth. The gas pressure he breathes always equals the water pressure. The diver becomes pressurized as he breathes in this gas.

This is why a diver must "decompress" before returning to the surface. If he doesn't, he could possibly die from the difference in pressure of air within his body and the atmosphere.