Ann Wochinski, age 16, of Watertown, N.Y., for her question:
WHEN WAS THE DEVONIAN PERIOD:
The Devonian period was the fourth division of the Paleozoic era of the geological time scale, spanning an interval from about 400 million to 350 million years ago, and it was named for Devonshire, a county in southwestern England where the sedimentary rocks of that period were first studied in the 1830s.
Scientists tell us the principal geological event of Devonian time was a three way collision between ancient land masses that were ancestral to North American and Eurasia, on the one hand, and Gondwanaland, the hypothetical supercontinent from which all the modern southern continents were formed.
Compressional forces generated by this collision folded and made mountains of thick sections of sedimentary strata that had accumulated in trough like zones of crustal weaknesses called geosynclines.
This Devonian episode of mountain building called the Acadian orogeny in North America and Greenland and the Caledonian orogeny, in Great Britain and Norway extended the Appalachian chain of mountains northward into New England and Canada.
Great volumes of coarse red sand and gravel were shed westward off the eroding flanks of these new Arcadian mountains and deposited on the stable platform of the continental interior, which was occupied intermittently by warm, shallow seas in which reefs of coral and sponge grew. These reef rocks eventually became locally saturated with petroleum, as was Devonian sandstone.
Great thicknesses of the red sand accumulated in a vast Catskill delta that buried and preserved the worlds first forest. Tall, slender trees, primitive leafy evergreens and ferns were included in this first forest.
Iron oxide cemented the sand grains together and colored them red, forming the Old Red Sandstone of the British isles and the Catskill red beds of Southeastern New York.
Scientists tell us that North America and Europe both straddled the equator during the Devonian period, whereas much of Africa and South America lay in the Arctic Zone. Under these climatic conditions, and with a newly formed atmospheric ozone layer for protection from deadly ultraviolet radiation, the first air breathing creatures ¬mites an spiders appeared on dry land.
In the seas, coiled shellfish called ammonoids, which were distant relatives to modern squid, were the first major form of invertebrate life.
Devonian fish, considerably evolved from the armor plated types of the preceding Ordovician period, now had fins and scales as well as jaws.
One group, the lobe fins, gave rise to the first air breathing vertebrates the amphibians which invaded the land at the close of Devonian time and set the stage for the advent of the reptiles in the Carboniferous period that followed.