First Steps Downward

Humans have tried to reach the ocean floor for thousands of years. Ancient Greek sponge divers held their breath to reach depths of about 30 meters. Alexander the Great reportedly descended in a glass barrel around 332 BCE. But the real barrier was always the same: pressure.

The diving bell — an inverted container trapping air underwater — was used from the 1500s onward. Edmund Halley (of comet fame) improved the design in 1691 by sending down weighted barrels of fresh air. Still, these devices barely scratched the surface compared to what lay below.