Paleozoic

The Paléozoïque is one geological era which extends from 540 to 250 million years. This era is sometimes called Primary era . Its beginning corresponds classically to the appearance of many fossils with hard shells, although one knows now that such animals exist since the previous era, the Édiacarien. This era is completed by a massive extinction.

Subdivisions

The Paleozoic one breaks up into 6 periods:

Stephen Jay Gould uses means Mnémotechnique S in order to retain the order of the geological periods easily. This sequence can be retained easily by a sentence giving the first syllables of the periods, of oldest with most recent, than one can want to pronounce by drinking Cahors ” (CAmbrien ORdovicien SIlurien DÉvonien CArbonifère PErmien).

There is also: “ Cambronne ordered silence and devotion to its police officers persons on leave ”, more complicated sentence but giving most of each name.

Paleogeography

The Paleozoic one starts shortly after the fragmentation of the Supercontinent Rodinia in at least eight continental masses. During this era these continents gather again to form Pangée.

Biotopes

At the beginning of this era the forms of life are limited to Bactérie S, Algue S, sponges and a variety of forms still badly known appeared during the Édiacarien. The diversity and the number of organizations explode during the Cambrien. It is thought that the first terrestrial organizations appear during the Paleozoic one but this phenomenon remains minor before the Silurien and the Dévonien. Although primitive Vertébré S are present at the beginning of this era the Invertébré S remain dominant until half of the Paleozoic one. The population of Poisson S explodes during the Dévonien. During second half of this era of large forests of primitive plants form what will become the modern coal seams. At the end of Paleozoic the first sophisticated reptiles and the first plants modern (Coniferous S) developed.

See too

geological time scale

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