Laura Ann Noll, age 12, Mayfield Heights Ohio,

How does natural gas get underground?

Natural gas can be playful dangerous and useful. It is the playful will‑o‑the‑whisp that dances with an eerie light over bogs and marshes,, It is the dangerous gas that sometimes explodes in an underground mine. It is the useful gas piped to do cooking duties in thousands of American kitchen ranges,

Though natural gas is mostly a mixture of gases, most of it is methane ‑alias marsh gas ‑ alias mine gas. Also present with the methane may be slight traces of butane, ethane, propane, helium and carbon‑oxide gases. This brew, called natural gas, arises from decay.. usually from rotting vegetation. It is given off as the complex plant cells break down into more simple chemicals.

Nature has been making natural gas for millions of years. Not all of it danced away in spooky will‑o‑whisps. Much of it is stored in hide‑sways deep underground. The U.S. is rich in buried natural gas. Most of it dates back to the third era of geological history which came to a close some 165 million years ago,

This Paleozoic ‑ old‑life ‑ era lasted some 320 million years. The seas were restless. Time after time they slopped over the lowlands and receded. And these ancient seas teemed with life. Tiny plants and animals thrived and multiplied in the warm, shallow waters. Time after time the sea receded and left them stranded in evaporating ponds and pools.

Sometimes the earth heaved and covered the drying mud under shelves of rocks and dirt. The marine animals and plants of the old marine life were trapped under the ground. Sometimes conditions were just right to imprison them for ages. Time, heat and pressure changed the remains. It became petroleum ‑ thick, black rock oil.

This fossilized oil often formed in the press of shales and other mud‑made rocks. The slow process of change and decay went on uninterrupted for millions of for millions of years. Methane and other gases were given off during this process of decay.

When possible, the gas merrily escaped through vents to the surface. But in some places, its too was trapped with the oil. The earth’s crust has buckled and bent. In some places, underground layers of rocks are bent to form arches. Maybe a layer of shale is sandwiched in an arch between two layers of dense rock. If the shale was once mud, teeming with ancient marine life, here is a likely place to look for petroleum.

In such a valuable pocket, the oil rests on salt water. Some clay salt water must be present to form petroleum. If the precious find is capped with a solid layer of dense rock, we may find natural gas resting above the oil. Through the long ages it was given off as waste in the process of making petroleum.