|
|
"Modern" Coal Plants
Nature Bulletin No. 331-A February 7, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
"MODERN" COAL PLANTS
The Age of Cycads, when those strange tree-like plants predominated,
began during the Triassic Period of the earth's geological history,
reached its peak during the 60 million years of the Jurassic Period
which followed, and ended during the first part of the Cretaceous
Period that began about 95 million years ago. During the Jurassic, in
addition to Cycades, there were also many species of ginkgos, and
conifers which were the ancestors of our modern sequoias and pines.
The ginkgo or "Maidenhair Tree", which we have imported from China
and Japan, is the only one remaining of that tribe -- "a living fossil".
Although enormous reptiles then dominated the land, the waters and the
air Jurassic rocks contain fossils of the first bird-like creature, many
insects, and a few mammals something like the living duck-billed
platypus. Also for the first time, annual growth rings appear in fossil
wood although the climate seems to have been growing warmer and
more humid over most of the earth.
During the Cretaceous Period the climate became uniformly warm and
humid from pole to pole and then, all over the earth, an entirely new
type of plants appeared. Previously, plants had reproduced by spores
(like ferns) or by naked seeds (like conifers). Some of these, like the
tree ferns, giant horsetails and cycads, had reached their climax and
virtually disappeared; many others, like the ferns and club mosses, had
dwindled in size and numbers to the minor importance they have today.
Suddenly, great numbers of flowering plants -- plants in which the seeds
are produced in a closed capsule or ovary -- appear as fossils in
Cretaceous rocks. No one knows how they began or why they spread so
rapidly and developed into so many thousands of species -- although the
great numbers of insects may have helped -- but, with an almost
explosive expansion, they took possession and dominated the plant
world, as they still do.
There were probably grasses, sedges, cattails, and the like, but such
plants, naturally, decayed quickly and there is little evidence of them.
There were Mary of our modern trees and shrubs, or their close
relatives. In sandstones formed during that period, now beneath Kansas
and neighboring states, are fossils of forests native today in the
subtropics. As far north as Greenland and Spitzbergen there were mixed
forests of ginkgos, conifers -- sequoias, junipers, pines and cypress --
and hardwoods including maples, oaks, walnuts, persimmons,
sycamores, tulip trees, eucalyptus, and even the breadfruit tree.
During the later part of the Cretaceous Period and the early part of the
succeeding Tertiary Period, the earth' s land surface was blanketed with
an amazingly luxuriant vegetation, just as it had been during the much
earlier Pennsylvanian Period, and there were tremendous deposits of
material which later became coal: especially lignite or brown coal.
During the middle Tertiary there was great volcanic activity. The Alps
and Himalayas were formed, and the Rockies were thrust up to a higher
level. Then the earth's climate gradually cooled. New plants appeared --
plants with soft non-woody stems that die clown after bearing seed but
send up new stems each year or grow from seeds -- plants that had
learned how to "dig in" and survive cold winters. Finally, about one
million years ago, the Ice Age began and there have been at least four
major advances and many retreats of great ice sheets from the polar
regions. In the warm intervals between glaciers, large beds of peat were
formed in many parts of the world, just as they are being formed today.
We may be living in one of those warm spells.
To return to the Nature Bulletins Click Here! |
|
Update: June 2012
|
|
