How is limestone formedl
Limestone is a rough, whitish rock. Great boulders and slabs of it sit on the ground and thick layers are buried deep under the surface. You would never guess that this pale, solid rock once teemed with life. But most of it was made by busy little creatures that lived and died millions of years ago. What's more, the limestone we find on the land was made in the sea.
The story of a thick layer of limestone may have started 50 million years ago. It began in a shallow sea where the waters teemed with trillions of very tiny animals. The children of these little animals still live in the waters of the modern world and the scientists call them foraminifera a name which means the window makers. The foraminifera of ancient days were also little window makers.
The ancient seas contained dissolved salts and other chemicals stolen from the land. The ancient foraminifera took limy calcite from the water to make shells in which to shelter themselves. Each left a little hole in the wall of his shell, a window through which he could keep in contact with the water which brought his food and oxygen. Countless trillions of the cells were made from calcite, the chemical known as calcium carbonate.
As they lived and died, countless numbers of these calcite shells fell to the floors of the ancient seas. They mixed with the mud and made thick, oozy carpets. But the old earth has often changed around her land and sea areas. Sometimes a sea became dry land. The little window makers wre left high and dry on top of their thick carpets of mud and shells.
In time the old sea bed became a stretch of dry land.
The oozy mud became dry, solid rock. The rock formed in this way was limestone. Where the water was clean and clear, the limestone turned out white. Where streams mixed muddy waters into the shallow sees, the dry limestone turned out to be greyish and dirty looking.
Some of our beds of limestone are along the Mississippi, far from the sea. They were started millions of years ago when the Arctic Ocean reached down and linked arms with the Gulf of Mexico. Some of our limestone is made by running water from calcite chemicals in the soil. These chemicals dissolve easily in water and, when the water dries up, they stay behind as solid rock. The stalagmites, stalactites and other fancy stone work in a limestone cave is made by dripping water. The calcite dissolves and stays behind when the water evaporates.
Limestone is easy to cut from its hiding places and the modern world has a million jobs for it to do. It helps to make iron and steel.
It is used to make the portland cement from which we make concrete. Calcite is one of the chemicals that can neutralize acids. For this reason, limestone is sometimes used as a fertilizer to help plants where there is too much acid in the soil.