Which is the largest ocean?

The Pacific covers about 165 million square kilometres, which is more than all the land on Earth put together, with room left over. It holds roughly half the free water on the planet, and at its widest it spans nearly half the globe - almost a third of the Earth's circumference of empty water.

Magellan named it. Having fought his way through the strait at the bottom of South America in appalling weather, he came out into water that happened to be calm and called it the peaceful sea. It was a bad sample. The Pacific is ringed by the most active volcanic and seismic belt on Earth and generates the largest tsunamis.

It contains the deepest point we know of, Challenger Deep in the Mariana Trench, at nearly 11 kilometres - Everest would fit inside with a couple of kilometres of water on top. And it is shrinking. The plates carrying it are being consumed at its edges faster than new floor is made, so the Pacific loses a few centimetres of width a year while the Atlantic gains.