The Devonian Period By Raul Maryann Geological Time

The Devonian Period By Raul & Maryann

Geological Time Scale The geologic time scale shows a chronologic measurement relating stratigraphy to time.

Life span of Devonian Period The Devonian period lasted 4 o 5 through 345 million years ago.

Continents The world's land was collected into two supercontinents, Gondwana and Euramerica. These vast landmasses lay relatively near each other in a single hemisphere, while a vast ocean covered the rest of the globe. These supercontinents were surrounded on all sides by subduction zones. With the development of the subduction zone between Gondwana and Euramerica, a major collision was set in motion that would bring the two together to form the single world-continent Pangea in the Permian.

Dominant Plant Life They lacked roots, leaves and structural strength to grow taller than a few feet; but all these features would be present by the end of the period enabling the growth of large trees and other plants.

Dominant Animal Life Placodermi: Their head and thorax were covered by articulated armored plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches. A 380 -million-year-old fossil of one species represents the oldest known example of live birth

Environment The Devonian was a warm period, and probably lacked any glaciers. The Devonian seas were dominated by brachiopods, such as the spiriferids, and by tabulate and rugose corals, which built large reefs in shallow waters. Encrusting red algae also contributed to reef building. Plants did not have roots or leaves like most plants today, and many had no vascular tissue at all. They probably spread vegetatively, rather than by spores or seeds, and did not grow much more than a few centimeters tall.

End of Devonian Period A mass extinction event occurred near the end of the Devonian. Glaciation and the lowering of the global sea level may have triggered this crisis, since the evidence suggests warm water marine species were most affected. Meteorite impacts have also been blamed for the mass extinction, or changes in atmospheric carbon dioxide. It is even conceivable that it was the evolution and spread of forests and the first plants with complex root systems that may have altered the global climate. Whatever the cause, it was about this time that the first vertebrates moved onto the land.

Bibliographical References • http: //www. ucmp. berkeley. edu/devonian. php • http: //science. nationalgeographic. com/science/prehistoric- world/devonian/ • http: //www. fossils-facts-and-finds. com/devonian_period. html