Welcome to You Ask Andy

Marvin Drake, age 12, of Concord, N.H., for his question:

HOW WAS NATURAL GAS FORMED?

Gas is one of our most important resources since we burn it to provide heat and to produce energy to run machinery. There are two kinds of gas: natural and manufactured. Most scientists say that natural gas was formed beneath the earth's surface billions of years ago. Almost all the gas used in the United States and Canada is natural gas.

Gas was first formed when water covered much more of the earth's surface than it does now. Down through the ages, great quantities of tiny marine plants and animals called plankton died and settled on the ocean floors.

On the ocean floors fine sand and mud drifted down over the plankton. Layer upon layer of these deposits piled up. The great weight of the plankton, plus bacteria, heat and other natural forces, changed the chemical compounds in the plankton into natural gas and oil.

The gas and oil then flowed into the holes in limestone, sandstone and other porous rocks. Layers of solid rocks formed over the porous rocks and sealed the gas and oil beneath.

Later, movements in the earth's crust caused the ancient seas to draw back and dry land appeared over many gas and oil deposits.

Pure natural gas is made up of chemical compounds of the elements hydrogen and carbon. These compounds are called hydrocarbons. Some hydrocarbons are naturally gaseous, some are liquid and some are solid. A hydrocarbon's form depends on the number and arrangement of the hydrogen and carbon atoms in the hydrocarbon molecule.

Natural gas is composed chiefly of methane, the lightest hydrocarbon. In a methane molecule, one atom of carbon is bound together with four atoms of hydrogen.

Manufactured gas is made chiefly from coal or petroleum, using heat and chemical processes. It costs more than natural gas and is used in regions where large amounts of natural gas aren't available.

The United States, Russia and Canada    in that order    are the world's leading producers of natural gas. Both Texas and Louisiana, the two chief producing states in the United States, produce more natural gas than Russia.

In the United States, manufactured gas accounts for only about one percent of the total gas consumed.

There are two chief types of manufactured gas: coke oven gas, which is sometimes called coal gas, and acetylene.

Coke oven gas is made by roasting coal. As the coal turns into coke, vapors consisting of many chemicals escape from the coal. The vapors are sent through water, which absorbs some of the unwanted chemicals. The rest of the gas bubbles up through the water. This gas may be further purified by various processes that remove byproducts.

Acetylene is produced chiefly by dropping water onto calcium carbide, a compound of calcium and carbon.

 

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