Photographs of the earth taken from lunar space
missions show it as a beautiful blue and white ball.
The blue is the ocean and the white swirls are the
clouds. The only planet in the solar system to have
oceans， the earth appears mainly blue because water
covers more of its surface than do the continents -
seventy-one per cent or almost three-quarters.
This water is not distributed evenly over the earth s
surface. Most of the land lies in the northern hemis-
phere， while most of the southern hemisphere is
ocean， with a continuous belt of water linking the
three major oceans.
The earth s three major oceans are the Pacific， the
Atlantic， and the Indian Oceans. The Pacific， which is
the largest， covers sixty-four million square miles -
about the same size as the Atlantic and the Indian
Oceans combined. It covers more than a third of the
surface of the earth and stretches almost half way
around it from east to west. It is so large that all the
land on the earth s surface could fit within its borders.
The Atlantic Ocean is next in size and although it
stretches as far north and south as the Pacific， it is
narrower and has an irregular shape， being 4500
miles across at its widest point， compared with
12，500 miles in the Pacific. The Indian Ocean is the
smallest of the major oceans， and is roughly triangu-
lar in shape. The Arctic is much smaller than the
major three and is covered almost entirely with ice.
The earth also has smaller water-covered areas
called seas， such as the Mediterranean and the
Caribbean. Seas may be part of an ocean - the Carib-
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