Paleozoic, Proterozoic, and Archeozoic Eras 



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Upper or 

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Lower or 

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CHARACTERISTICS OF THE TIMES 

 AND VARIOUS TYPES 



Periodic glaciation; elevation of 

 continents ; several climatic 

 changes; aridity pronounced 



Rise of land vertebrates and mod- 

 ern insects; rise of ammonites 

 (Mollusca with coiled, cham- 

 bered shells) 



Coal-forming plants common; 

 earliest reptiles, amphibia, fishes ; 

 mollusks, arthropods (crayfishes, 

 beetles, cockroaches, centipedes, 

 spiders), echinoderms 



Coal-forming plants common 

 Amphibia, fishes, mollusks, cri- 

 noids (coelenterates) 



Rise of amphibia, crabs, and 

 snails; bony fishes, brachiopods; 

 Mayflies; abundant mollusks; 

 decline of trilobites 



Many parts of the world very 

 arid; rise of air-breathing ani- 

 mals (as insects, scorpions, etc.) 



Abundant corals (coelenterates), 

 armored fishes, mollusks, bra- 

 chiopods, decline of trilobites 



Rise of land plants, rise of fishes 

 (cartilaginous and sharklike), 

 rise of corals (coelenterates), 

 brachiopods, trilobites 



Only invertebrate animals present ; 

 segmented worms, mollusks; rise 

 of brachiopods, echinoderms, 

 jellyfishes, sponges, corals ; 

 abundant trilobites 



Rise of primitive, multicellular 

 invertebrate animals; very few, 

 imperfect fossils; traces of 

 marine algae, bacteria, shelled- 

 protozoa, coelenterates, seg- 

 mented worms, sponges, and 

 trilobites 



Rise of simple, primitive, unicel- 

 lular types; large deposits of 

 limestone, graphite, and iron 

 ores of unicellular origin; no 

 fossils remain, if any w^ere ever 

 formed 



REPRESENTATIVE LIFE 





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Fig. 322. — Description of the periods and epochs of the Paleozoic, Proterozoic, 

 and Archeozoic Eras of geologic time. Representatives of life during these times 

 are shown at the right. (Not drawn to scale.) (Compare with Fig. 320.) 



