However, the Pacific is not always peaceful. Its islands are often hit by typhoons, and the countries surrounding it have many volcanoes and are often hit by earthquakes. Tsunamis

　　(海啸 ), caused by underwater earthquakes, have destroyed many low－lying coastal towns.

　　The Ocean contains about 46% of Earth’s surface water, and makes up about 32% of its total surface area, more than all of the planet’s land areas.

　　The equator (赤道) divides it into the North Pacific and the South Pacific Oceans, the latter of which contains most of its largest 25,000 islands. The largest landmass entirely within the Pacific Ocean is the island of New Guinea, with Australia to its south；it has been the world’s second－largest island since separating from the Australian mainland.The lowest point on Earth, the Mariana Trench (海沟), lies 10,911 meters below the surface of the Pacific, but the Ocean’s average depth is 4,280 meters.

　　The water temperature of the Pacific varies from freezing at the poles to about 300C near the equator. Its salinity (盐分) also varies from place to place. The water near the equator is less salty because of the rainfall there, but at the poles salinity is also low, because little evaporation (蒸发) takes place in the cold water of these areas.

　　The exploitation (开采) of the Pacific’s mineral wealth is difficult in its deeper parts. However, in the shallow waters of the continental shelves off the coasts of Australia and New Zealand, oil and natural gas are exploited, and pearls are harvested along the coasts of Australia, Japan, Nicaragua and the Philippines.

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