The Mariana Trench contains the deepest known point in the ocean floor.

The longer version

Ocean trenches form where one plate slides beneath another, bending the seafloor down into a long, narrow trough. The subducting slab drags the crust downward faster than sediment can fill the gap, producing depths far greater than anywhere on land. Trenches often run parallel to chains of volcanic islands.

Pressure at the bottom is immense, equal to the weight of a tall column of water pressing on every surface. Yet life persists there, with small organisms adapted to darkness, cold and weight. Water temperature hovers just above freezing. Exploration is difficult and costly, so most of the trench has been mapped by sound rather than visited by people.

Where this entry sits

These facts wander across maps, borders, deserts, rivers, mountains, and the extreme corners of the natural world. Each one is short and self-contained, offering a small surprise about places you may never visit rather than anything you actually need. The full list sits on the Geography page, where every entry is listed in order.