Sharks are essentially living fossils, having glided through the Earth’s oceans for over 400 million years already. They have outlasted the dinosaurs and have survived mass extinction events to become one of the most successful and enduring groups of animals on the planet.

At three hundred feet, we are profoundly changed. The pressure at these depths is nine times that of the surface. The organs collapse. The heart beats at a quarter of its normal rate, slower than the rate of a person in a coma. Senses disappear. The brain enters a dream state. At six hundred feet down, the ocean’s pressure—some eighteen times that

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