Charles Cooper, age 11, of Tulsa, Okla., for his question:
How is natural gas formed?
It is the playful will‑.‑the‑wisp that dances with a spooky glow over the twilight bogs and marshes. It is the angry gas that sometimes explodes with destructive fury in an underground mine. It is also the very useful cooking gas that is piped to light the ranges in countless kitchens across the land. Mother Nature has been making this natural gas for millions of years and the process is still going on.
Natural gas is an assorted mixture. It contains a lot of methane, alias marsh gas, alias mine gas. This is the tricky substance that trips over the swamps as a will‑o‑the‑wisp and sometimes explodes underground in a mine. Mixed with the methane, we usually find smaller amounts of butane, ethane, propane, helium and carbon dioxide. In the list you will notice the names of some useful gases we have been able to put to work for us.
The strange brew called natural gas often arises from decaying material, often from rotting vegetation. It may be given off as waste as the complex plant cells break down into more simple chemicals. This is why it appears as a spooky light arising from the decay in a stagnant marsh. We are not certain, but most people think that the natural gas buried in the ground also arose from decaying material,
Many scientists think that the story of our buried natural gas may have started in the Paleozoic Era, about 165 million years ago. The ancient seas were then restless and time after time they slopped over the lowlands and receded. Tiny plants and animals thrived in the waters and the shallow seas teemed with life. Time after time, the water with its ancient marine life was left behind to evaporate in oozy ponds and pools.
Sometimes the earth heaved her rocky shoulders and covered the old sea beds with dirt and debris.
The oozy remains of the ancient sea dwellers became covered with layers of new rock and perhaps were imprisoned for ages. The heavy surface rocks smothered the muddy ooze with heat and pressure. In time, the ancient marine fossils were changed into petroleum. The changes may have been similar to decay, though much slower.
If this is so, methane and other gases would be given off, rise up and seep through porous rocks into the air. But sometimes the mixture was trapped, say, under a dense dome of shale and the gases, too, were trapped. This is the kind of formation where natural gas is most often found. It sits under a dense, rocky roof on top of a layer of petroleum soaked rocks below it.
Tide are almost, though not quite, sure that this is how our natural gas was formed, When the rocks about petroleum are light and porous, the gases from the decaying fossil material seeped out and were lost. We find them only where the petroleum has been securely capped for countless ages under a dense roof.