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What Is the Origin of Oil?
| Article
# : |
15891 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
1 / 1989 |
4,458 Words |
| Author
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Marc J. Defant
Marc J. Defant is professor of geology at the University of
South Florida. He specializes in the study of volcanoes and is
the author of Voyage of Discovery: From the Big Bang to the
Ice Ages, a panoramic history of the universe, including our
galaxy, solar system, and planet. |
In the late 1800s, Santa Barbara, California, and the nearby Channel Islands (now a national park) were popular health resorts. People went there to breathe a "purified" atmosphere that was thought to have medicinal benefits. The pungent odors were produced by natural oil and gas seeps from sedimentary rock deposited some 12 million years ago.
Ninety miles south of Santa Barbara, the La Brea Tar Pits in downtown Los Angeles--still active but now enclosed by a high fence--is another natural oil seep. Such natural oil seeps are not uncommon nor, contrary to folklore, are they necessarily beneficial for one's health. For hundreds of millions of years and perhaps longer, hydrocarbons (molecules composed of carbon and hydrogen in various proportions) have been escaping at the earth's surface, either as natural gas, oil, or tar, depending on the weight of the hydrocarbon molecules.
The La Brea Tar Pits is the result of the evaporation of the lighter hydrocarbons from a natural oil seep, leaving tar, the heavier hydrocarbons. The water and vegetation that formed on top of this sticky accumulation in the last million years must have attracted many herbivores, including the mastodon and giant ground sloth which became trapped in the tar. The death cries of these herbivores would also have attracted carnivores like saber-toothed tigers, lions, wolves, and bears, which have all been entombed in this asphalt grave.
The oil that seeps to the surface is just a small proportion of the vast amounts that reside within the earth. Known petroleum reserves are approaching two trillion barrels. Where did all this oil come from? The currently accepted biogenic theory of the origin of oil is that organic matter became buried in sediments, and subsequent conditions of pressure, temperature, and time transformed this organic matter to oil. Thus oil has been classified, along with coal, as a fossil fuel.
Since 1979, however, an opposing abiogenic theory of the origin of oil has been strongly promulgated by Thomas Gold, the John L. Wetherill Professor of Astronomy at Cornell University. "Calling them fossil fuels is a misnomer," says Gold. "Almost all of our oil and gas have nothing to do with organic decay; they've been present deep inside the Earth ever since the planet was created, and we're not even close to running out."
Oil From Buried Organic
...
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