Devonian Period (World of Earth Science)
In geologic time, the Devonian Period, the fourth period of the Paleozoic Era, covers the time roughly 410 million years ago (mya) until 360 mya.
The Devonian Period spans three epochs. The Early Devonian Epoch is the most ancient, followed in sequence by the Middle Devonian Epoch, and the Late Devonian Epoch.
The Early Devonian Epoch is divided chronologically (from the most ancient to the most recent) into the Gedinnian, Siegenian, and Emsian stages. The Middle Devonian Epoch is divided chronologically (from the most ancient to the most recent) into the Eifelian and Givetian stages. The Late Devonian Epoch is divided chronologically (from the most ancient to the most recent) into the Frasnian and Famennian stages.
In terms of paleogeography (the study of the evolution of the continents from supercontinents and the establishment of geologic features), the Devonian Period featured continued cleavage of supercontinent landmass and fusion of plates into the supercontinent Laurasia and eventually the supercontinent Pangaea.
Differentiated by fossil remains and continental movements, the Silurian Period preceded the Devonian Period. The Devonian is followed in geologic time by the Carboniferous Period (360 mya to 286 mya). In many modern geological texts, especially those in the United States, the time of Carboniferous Period covered by two alternate geologic periods, the Mississippian Period (360 mya to 325 mya) and the Pennsylvanian Period (325 mya to 286 mya). A mass extinction marks the end of the Devonian Period. In accord with a mass extinction, many fossils dated to the Devonian Period are not found in Carboniferous Period (i.e., alternatively, Mississippian Period and Pennsylvanian Period) formations.
The Devonian Period marked a geologically active period. The North American and European continentsith more tropical climates due to more equatorial positionsrifted together. As a result, the two continents share a similar fossil record for the Devonian Period. Similar fossil finds dating to the Devonian Period are found in Germany, Canada, and the United States.
The fossil record indicates that it was during the Devonian Period (also termed the "Age of Fishes" because of the appearance of sharks and bony fishes) that amphibians and more terrestrial (land based) vertebrates evolved. Seed plants also appeared, continuing a diversification and development of botanical species, especially vascular plants. By the end of the Devonian Period, the first forests appeared.
There were a number of major impacts from large meteorites that date to the Devonian Period. Similar to the K-T event, many scientists argue that these impacts could have provided the environmental stresses that eliminated approximately 25% of Devonian Period species. Impact craters dating to the Devonian Period have been identified in modern China, Canada, Russia, and Sweden.
See also Archean; Cambrian Period; Cenozoic Era; Cretaceous Period; Dating methods; Eocene Epoch; Evolution, evidence of; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Miocene Epoch; Oligocene Epoch; Ordovician Period; Paleocene Epoch; Phanerozoic Eon; Pleistocene Epoch; Pliocene Epoch; Precambrian; Proterozoic Era; Quaternary Period; Tertiary Period; Triassic Period