Deon Storlie, age 12, of Cloquet, Minn., for his question:
HOW IS CORAL ROCK FORMED?
The crusty surface of the earth is made from hundreds of rocky minerals. Most of the rocks were modeled and remodeled from simple minerals by the restless crust, as sediments sank in the seas or as mountains arose to be eroded by the weather. But in order to create coral rock, the earth needed some extra help.
Coral rock is made mostly from chalky minerals called calciums. The story of its creation begins with the running rivers that dissolve calcium and other minerals from the land and dump them into the ocean. There these minerals are absorbed by a multitude of sea dwellers who use them to build their bones or shells.
Our story takes us down to a watery world, teeming with small creatures called coral polyps. They have soft, boneless bodies, hollow stomachs and circles of tentacles arranged in multiples of six. Though there are hundreds of coral species, most of them are smaller than one inch
Adrift in the hungry sea, the helpless little corals would soon perish. However, we know for a fact that they have survived successfully through hundreds of millions of years because they were able to absorb calcium from the water and use it to build themselves chalky homes. When they departed, their homes survived as coral rock.
A few coral species live in cool northern waters, and a few live solitary lives, surviving in cuplike shells. But a great majority live in crowded communities, somewhat like apartment dwellers. And a great majority live in tropical seas, where the water temperature rarely dips below 70 degrees Fahrenheit.
They prefer shallow coastal regions, usually where the sea bed is no more than 100 feet or so below the waves and tossing tides. Each young coral builds its own chalky cup, and each generation adds a new layer to the outside of the family apartment house. After many generations and countless ages, this becomes a sizable chunk of chalky coral.
Through millions of years, the various polyps formed thick layers of chalky coral and then departed. Often the deserted structures are broken apart by pounding waves and cemented with muddy silt to form hardened coral rock. In warm climates, this material often is sliced into blocks to build homes for humans.