Anna Louise Cipollone, age 12, of Pittsburgh, Pennsylvania, for her question:

How are islands formed?

One might suppose that the earth uses one, and only one, recipe to build her sea circled islands. Not at all. Islands are formed in many different ways. Nobody has counted all the large and small islands that exist on our watery world. Certainly no two of them are exactly alike and every one has a history of its own.

Some islands are formed when the seabed rises, hoisting them high and dry above the water. Others are formed when part of a continent sinks below the sea, leaving an island of high ground above the new water level. Some islands are built by under¬sea volcanoes, patiently piling up cinders and lava until the peak rises above the water. Others are formed by growing undersea mountains that finally hoist their highest peaks above the waves.

Some of the most interesting islands are made of rocky coral, built by generations of little polyp creatures. Sometimes they form along tropical and semi tropical shores, where coral reefs finally grow tall enough to remain above the tides. More often they are coral atolls, where masses of stony coral form a crescent around the rim of a submerged volcano.

Recently a most dramatic new island appeared in the northern Atlantic. The sudden event began when an undersea volcano erupted with sound and fury. Clouds of steamy fumes poured into the air, rivers of red hot lava seethed to the surface. After a series of these eruptions, the cooling lava built a cone large enough to form a new volcanic isle.

Islands of this sort may be formed in a few weeks or even days. On the other hand, it may take a million years or more to build a coral island. After all, the soft coral polyps are very, very small. The chunky coral stone is a family apartment house and each young polyp builds his own apartment on the mass of numerous apartments built by his departed ancestors.

Then there are larger islands, one of them big enough to be rated as a continent. Sea circled lands such as Australia and Greenland have another and very different story to tell. Many millions of years ago, all the earth's dry land formed a single continent; maybe somewhere near what is now the South Pole.

Through the ages, this original continent cracked and the sections drifted apart, like rafts through the world ocean. Eventually, one of the separated pieces became Australia, another became Greenland.

The earth is a watery world and most of its surface is and, for a large part of its history has been, covered by water. The original land mass must have been an island continent, for the sea surrounded it on every side. Though the original water now is partitioned with land areas, it seas still merge to form a global ocean. So we might regard the major land masses as large, sea surrounded islands that formed when the original continent split and its fragments drifted apart.