The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian-Triassic Extinction Event. The effects of this catastrophe were so devastating that it took life on land 30 million years to recover.[1] Recovery of life in the sea may have been much faster.[2]
Contents[hide] |
[edit] Geology
During the hiatus between the late Precambrian and the Paleozoic most of the evidence of the earth's early history was destroyed by erosion.[citation needed] From the beginning of the Paleozoic, shallow seas began to encroach on the continents, large parts of North America were completely submerged.In North America, the era began with submerged geosynclines, or deep basins of the Earth's crust, along the eastern, southeastern, and western sides of the continent, while the interior was dry land. As the era proceeded, the marginal seas periodically washed over the stable interior, leaving sedimentary deposits to mark their incursions. During the early part of the era, the area of exposed Precambrian, or shield, rocks in central Canada were eroding, supplying sediment to the geosynclines from the interior. Beginning in the Ordovician Period, mountain building intermittently proceeded in the eastern part of the Appalachian geosyncline throughout the rest of the era, bringing in new sediments. Sediments washing from the Acadian Mountains filled the western part of the Appalachian geosyncline to form the famous coal swamps of the Carboniferous Period.
Paleoclimatic studies and evidence of glaciers indicate that central Africa was most likely in the polar regions during the early Paleozoic. During the early Paleozoic, the huge continent Gondwanaland had either formed or was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent Pangaea and resulted in some of the great mountain chains, including the Appalachians, Urals, and mountains of Tasmania.
[edit] Animal Life
A noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the invertebrate animal phyla in great abundance at the beginning of the Cambrian. A few primitive fishlike invertebrates, and then vertebrates, appeared in the Cambrian and Ordovician, scorpions in the Silurian period, land invertebrates and amphibians in the Devonian, land reptiles in the Carboniferous, and marine reptiles in the Permian.Amphibians were the dominant vertebrates until the mid Carboniferous, then climate change greatly reduced their diversity; meanwhile reptiles prospered and continued to increase in number and variety by the late Permian.[3]
[edit] Plant Life
Plant life of the Paleozoic era reached its climax in the Carboniferous, when towering lycopsid rainforests dominated the tropical belt of Euramerica. Climate change caused the Carboniferous Rainforest Collapse which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian.[3][edit] Tectonics
[edit] Climate
The Ordovician and Silurian periods were warm greenhouse periods, with the highest sea levels of the Paleozoic (200 m above today's); the warm climate was interrupted only by a ~30 Ma cool period, the Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation.[4]  | This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2007) |
The Middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the Ice Age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, oxygen levels increased and carbon dioxide dropped, although much less dramatically. The north-south temperature gradient also seems to have moderated, or metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses which killed off much of Middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.
The Late Paleozoic was a time which has left us a good many unanswered questions. The Mississippian epoch began with a spike in atmospheric oxygen, while carbon dioxide plummeted to unheard-of lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician Ice; but, this time, the effects on world biota were inconsequential. By the Cisuralian, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangea created huge arid inland areas subject to temperature extremes. The Lopingian is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.
[edit] See also
 | Wikimedia Commons has media related to: Paleozoic |
[edit] References and further reading
- ^ Sahney, S. and Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC 2596898. PMID 18198148. http://journals.royalsociety.org/content/qq5un1810k7605h5/fulltext.pdf.
- ^ url=http://www.economist.com/node/16524904
- ^ a b Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1. http://geology.geoscienceworld.org/cgi/content/abstract/38/12/1079.
- ^ Munnecke, A.; Calner, M.; Harper, D. A. T.; Servais, T. (2010). "Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology 296 (3–4): 389–413. doi:10.1016/j.palaeo.2010.08.001.
- British Palaeozoic Fossils, 1975, The Natural History Museum, London.
- "International Commission on Stratigraphy (ICS)". Home Page. http://www.stratigraphy.org/. Retrieved September 19, 2005.
| Preceded by Proterozoic Eon | 542 Ma - Phanerozoic Eon - Present | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 542 Ma - Paleozoic Era - 251 Ma | 251 Ma - Mesozoic Era - 65 Ma | 65 Ma - Cenozoic Era - Present | ||||||||||
| Cambrian | Ordovician | Silurian | Devonian | Carboniferous | Permian | Triassic | Jurassic | Cretaceous | Paleogene | Neogene | Quaternary | |
| ||
Walang komento:
Mag-post ng isang Komento