The Pacific Ocean

The Pacific covers approximately 155 million square kilometres and is by far the largest of the world's ocean basins.

It covers more than 30 percent of Earth's surface.

It averages about 4,000 metres deep, deeper than the 3,682 metre average for the ocean as a whole.

Ferdinand Magellan named the ocean in the 16th century. He called it pacific, meaning peaceful, because of the calm water he met.

Magellan, a Portuguese navigator in the employ of Spain, began his voyage in 1519 in search of a western route to the Spice Islands. His fleet entered the ocean in November 1520.

The Challenger Deep, the deepest known part of the ocean, lies in the Mariana Trench in the western Pacific.

Estimates of its depth differ slightly: about 10,935 metres in one NOAA account, and 10,994 metres, plus or minus 40 metres, in a 2010 University of New Hampshire survey.

The Mariana Trench is more than 2,550 kilometres long and 69 kilometres wide on average.

The first sounding came in 1875 from the crew of the British Royal Navy expedition aboard HMS Challenger, who recorded 8,184 metres with a weighted rope.

A British survey vessel, Challenger II, surveyed the trench in 1951, and Japan sent a survey vessel to map it in 1984 with a multibeam echo sounder.

Mount Everest, 8.84 kilometres high, would not break the surface if placed in the Mariana Trench.

In 2012 the film director James Cameron made a solo dive to the bottom of the Challenger Deep. Most of the trench has been a US protected zone since 2009.

The Pacific basin is called the Ring of Fire because of intense earthquake and volcanic activity around its edges. Volcanic arcs and ocean trenches partly encircle it.

The Ring of Fire, also called the Circum-Pacific Belt, is approximately 40,000 kilometres long and is marked by active volcanoes and frequent earthquakes.

It follows the boundaries of the Pacific, Juan de Fuca, Cocos, Indian-Australian, Nazca, North American and Philippine plates. The boundary between the Pacific and North American plates is a significant exception, because it is a transform boundary.

Geologists count a volcano as active if it has had a recorded eruption since the last glacial period, about 10,000 years ago.

The East Pacific Rise spreads at 6 to 16 centimetres a year, faster than the Mid-Atlantic Ridge at 2 to 5 centimetres a year.