( mya )
The Paleozoic , even Palaeozoic or Erdaltzeit , is the oldest of the three eras in which the Aeon Phanerozoic in the geological time scale is divided. It covers the period from approx. 541 million years to approx. 251.9 million years before today. The Mesozoic (Earth Middle Ages) followed the Paleozoic .
History and naming
As early as 1838, Adam Sedgwick introduced the term in its English equivalent as the palæozoic series to classify the stratified rocks in the reclining area of the "Old Red" in England. According to its definition, the Paleozoic only included the Lower and Upper Cambrian and the Silurian. Roderick Impey Murchison , together with Count Alexander Keyserling and Édouard de Verneuil, succeeded in proving after a trip through Russia that the Paleozoic also included the Permian. They thus established the classification that is still in use today.
Classification of the Paleozoic Era
Position of the Paleozoic Era in the Phanerozoic Era:
Eon : Phanerozoikum (541-0 mya )
- Era : Cenozoic (Earth Modern Age) (66–0 mya)
- Era: Mesozoic ( Mesozoic Ages) (251.9–66 mya)
- Era: Paleozoic (ancient times) (541-251.9 mya)
The Permian, Carboniferous, and Devonian periods are informally grouped together as the Young Paleozoic , while the Silurian, Ordovician, and Cambrian periods are collectively referred to as the Old Paleozoic .
Before the Cambrian lies the so-called Precambrian . It covers the eons from the formation of the earth approx. 4600 mya up to the beginning of the Phanerozoic, i. H. 90% of the earth's history. These are the Proterozoic (2500–541 mya), the Archean (4000–2500 mya) and the Hadaic. (4600-4000 mya).
Life in the Paleozoic
The earliest Paleozoic Era is characterized by the appearance of the so-called small shelly fauna in the lower Cambrian. These hard-shelled organisms, often only a few millimeters in size, developed very different shapes and have been detected worldwide. In the course of the Cambrian Explosion , almost all of the animal kingdoms that still exist today developed .
Life was initially limited to the oceans . First reef formers who already were from the Precambrian known algae formations ( stromatolites ). But larger, more complex reefs emerged as early as the Middle Ordovician . At the end of the Ordovician, at the height of the Upper Ordovician glaciation, there was a mass extinction . A diverse marine reef community is known from the Silurian ( stromatopores , corals , bryozoa ). Remains of the first Silurian land plants ( Psilophyta ) have been handed down, although the colonization of the continents by moss-like plants ( bryophytes ) and early fungus forms probably began as early as the Middle Cambrian and continued increasingly in the Ordovician.
Reef communities continued to develop during the Devonian. In Germany, which at that time was in the tropical climate zone near the equator, the limestone basins of the Eifel and Sauerland are an example of this. From the Upper Devonian strata it can be seen that life had already conquered the land: the first amphibians have come down to us that lived at least partially on land. In the Upper Devonian, the Kellwasser and Hangenberg events resulted in two major mass extinctions that killed up to 75 percent of ocean life.
In the Carboniferous the continents were already populated by a diverse fauna and, mainly in the area of the equator and on the coastal regions, large areas of the forests, whose fossils can be found today in the coal seams. Above all, arthropods recorded in the oxygen-rich atmosphere of the Carboniferous an increase in size that was no longer achieved later, for example the giant dragonfly Meganeura or arthropods such as Arthropleura , which lived in the warm and humid climate of extensive swampy landscapes.
Over large parts of the Carboniferous and up to about the Middle Permian, especially in the southern hemisphere, the cold- age conditions of the Permocarbon Ice Age prevailed , with a duration of 80 to 100 million years the second longest ice age in the history of the earth. Initially, only the mainland areas of the greater continent Gondwana, which were close to the polar regions , were covered by large ice sheets before the glaciers temporarily advanced to the 40th parallel south of the country. The geographic range of many tropical marine species was limited to the Tethys , a gulf-like sea that protruded from the east into the supercontinent Pangea , which was formed about 310 million years ago when the land masses of Gondwana and Laurussia merged .
After the forest landscapes lost their surface several times during various glacial phases towards the end of the Carboniferous, the increasingly arid climate resulted in the extensive collapse of the tropical rainforests and the associated reduction in wetlands and swampy areas 305 million years ago . Arthropods, a large part of the amphibians of that time and early reptiles with a semi-aquatic way of life were particularly affected by the loss of these biotopes . As a result of the fragmentation of the habitats, the biodiversity of the terrestrial vertebrates declined significantly on the Carbon-Permian border and initially remained low in the early Permian, before the biodiversity gradually increased again in the further course. The largest land-dwelling animals in the Permian were the therapsids , the "mammal-like reptiles".
At the end of the Paleozoic Era, on the Permian-Triassic border , the greatest mass extinction in the history of the earth occurred, during which over 90 percent of marine species and around 75 percent of species living on land became extinct. The duration of the biological and ecological crisis was given in the older scientific literature to be several hundred thousand years; according to an analysis published in 2014, this time window is reduced to two core areas of 60,000 years each (± 48,000 years). On the other hand, a study published in 2018 came to the conclusion that the immediate crisis period spanned a maximum of 30,000 years, possibly limited to a few millennia. The goniatites , forerunners of the ammonites that were later successful in the Mesozoic Era , narrowly escaped extinction. Only two or three species survived the transition from the Permian to the subsequent Triassic . The trilobites , which have been widespread since the Cambrian, died out completely along with many other species. Geological findings and isotope analyzes speak for a very rapid global warming with numerous consequences as a possible cause of mass extinction.
- Steven M. Stanley: Turning Marks of Life. Spektrum Akademischer Verlag, Heidelberg 1998, ISBN 3-8274-0475-4 .
The paleomap-project on http://www.scotese.com offers plate tectonic reconstructions of the continent arrangement in the Paleozoic:
- Cambrian: http://www.scotese.com/newpage12.htm
- Ordovician: http://www.scotese.com/newpage1.htm
- Silurian: http://www.scotese.com/newpage2.htm
- Devon: http://www.scotese.com/newpage3.htm
- Carbon: http://www.scotese.com/late.htm
- Perm: http://www.scotese.com/newpage5.htm
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