Before the beginning of the 1900s, the only way to obtain pearls was by collecting very large numbers of pearl oysters from the ocean floor by hand. The oysters - or sometimes mussels - were brought to the surface, opened, and searched . More than a ton of these had to be checked in order to find just three or four quality pearls. Divers often descended to depths of over 100 feet on just one single breath. Now, of course this exposed them to hostile creatures and dangerous waves, not to mention drowning. In some areas, divers put grease on their bodies to conserve heat and they held a large, object like a rock, to descend so they didn't have to exert effort going down. Today, pearl diving has pretty much been supplanted by cultured pearl. Particles are implanted in the oyster to encourage the formation of pearls farms, and this allows for more predictable production. The divers who still work, do so mainly for the tourist industry.