At the bottom of the Mariana Trench, roughly 10,935 meters below the Pacific surface, water temperatures hover just above freezing and no trace of sunlight has reached the seafloor for as long as ...

Water temperatures barely above freezing, pressure exceeding 16,000 pounds per square inch, and depths past 10,000 meters define the Challenger Deep, the lowest known point on Earth’s surface.

What would ocean basins look like, if we drained away all of the water? Like a big bathtub, with a wide, flat bottom in the middle? Or like a round bowl, with the deepest spot at the very middle?

I spent years preparing to dive into the deepest place on Earth. Only a handful of people have traveled into the depths of the Mariana Trench, nearly 7 miles below the ocean surface. As a geologist ...