Dive beneath the ocean's waves, past the sunlit, teeming waters near the surface, through the oxygen-deficient zones nearly devoid of life, down, down and down some more, to a place where the pressure would crush a human, and you will find the mysterious, alien world of the deep sea.
It is 300 times the size of the space inhabited by Earth's land-dwelling species. It is unimaginably cold and cloaked in near-total darkness.
Despite the fact that this alien world is relatively accessible compared with the planets even in our own solar system, the deepest depths of the ocean remain virtually unexplored the final, mysterious frontier of our home planet.
Although the deep sea roughly defined as everything below 650 feet (200 meters) comprises a stunning 240 million cubic miles (1 billion cubic kilometers) and more than 90 percent of the living space on the planet, scientists are still trying to answer the most basic questions about it.