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The Origin of Coal
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18193 |
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Section : |
NATURAL SCIENCE
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| Issue
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11 / 1990 |
2,846 Words |
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Jennifer M. Robinson
Jennifer M. Robinson is a research associate at the Earth
System Science Center at Pennsylvania State University. |
The greatest coal age in Earth history came in the Late Paleozoic era, between 320 and 250 million years ago. The first part of this period, the Carboniferous, produced much of the coal in Europe and North America. It is portrayed as a time of vast warm tropical swamps, with dragonflies with two-foot wingspans, and giant club moss trees. The second part, the Permian, yielded more coal, but is less familiar to us because the coal was deposited in Siberia, Australia, China, and India. Unlike Carboniferous coals, Permian coals were formed in cool climates. The forests that produced them were much more like modern forests than the giant club moss forests of the Carboniferous. Their dominant trees were ancient relatives of modern Southern Hemisphere conifers, but unlike those of today, most of them had broad leaves. The second great coal age, that of the Cretaceous and Early Tertiary, had rates of coal formation that were only about half those of the Late Paleozoic.
Why was this time of geologic history, just before the emergence of the dinosaurs, so peculiarly prolific in depositing coal within the earth? Various ideas have been proposed, but each has suffered serious deficiencies. Recently, new evidence suggests that those ancient trees could resist decay allowing their carbon to be deposited and compressed into black lumps of energy - and simultaneously changing the earth's chemistry and climate.
Coal and geochemistry
The late Robert Garrels, one of the foremost geochemists of this century, pioneered the now-flourishing study of global biogeochemical cycles; he developed a model to study global balances of carbon, sulfur, iron, and
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