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The oceans cover more than two-thirds of the surface of Earth, with

an average depth of 3.8 km (2.4 miles), but they are not just

huge pools of salt water. The ocean floors are where

the great plates of Earth’s crust are splitting

apart or grinding together, creating long,

high ridges and deep trenches

dotted with volcanoes. As a

result of this, the oceans are

changing their size and

shape all the time.

Oceans

164

PACIFIC

OCEAN

As big as all

other oceans

put together,

the Pacific is

shrinking as the

edges of its floor

slip into deep ocean

trenches like the Mariana

Trench. The East Pacific

Rise, however, is the most

active mid-ocean ridge, spreading

at up to 22 cm (8.5 in) a year.

Aleutian Trench

Sargasso Sea

Gulf of

Mexico

Caribbean

Sea

Hudson Bay

Hawaii is just

one of many

volcanic

Rocks and

seamounts

ATLANTIC OCEAN

The Atlantic formed when North and

South America split from Europe and Africa

and gradually moved west. The ocean is still growing

as new ocean floor is created at the Mid-Atlantic

Ridge. The ridge breaks the surface in the north to

form Iceland, with its volcanoes and geysers.

Iceland

East Pacific Rise

Peru-Chile Trench has

been created by the

Pacific floor sliding

under South

America

Mid-Atlantic Ridge

has been built up

by a spreading rift

in the ocean floor

Arctic Ocean

Pacific Ocean

Atlantic

Ocean

Atlantic

Ocean

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