The Paleozoic

Cambrian Period 541-485 MYA Named by Adam Sedgewick as a Latinized form of Welsh name for Wales (Cymru). Period begins with the breakup of a supercontinent called Pannotia, centered on the south pole Increase in the number of animals with hard exoskeletons. It likely began as a way to sequester Ca, but continued with larger body sizes following predation. CO2 (~1.4%) O2 (rose to ~14%)

Ordovician Period 485-443 MYA Named after a Celtic Welsh tribe by Charles Lapworth to resolve a fight between Sedgewick and Murchison Transition from Cambrian marked by an extinction event To Silurian by a more significant extinction event (~60% lost) Continents remained southern in distribution

Silurian Period 444-416 MYA Roderick Murchison named this rock sequence after an ancient Celtic tribe of Wales Continental masses equatorial and began to collide Vascular plants appeared on land Jawless fish continued to diversify and jaws appeared

Devonian Period 419-358 MYA Named after Devon, England by Murchison and Sedgewick Vascular plants diversified Vertebrates began to move onto land End of the period marked by a series of extinctions

Carboniferous Period 358-298 MYA Named for coal-bearing strata by William Conybeare and William Phillips Mississippian (358-323 MYA) Pennsylvanian (323-298 MYA) Southern continents (Gondwana) were centered over the south pole generating a southern hemispheric ice age Romer’s Gap (360-345 MYA) caused by mass extinction and drop in oxygen Rise in importance of ray-finned fishes and crinoids Gradual rise in oxygen to 35% as more carbon sequestered Rise in terrestrial arthropods, amphibians and reptiles Toward the end of period (~305 MYA) rainforest collapse –a minor extinction event

Permian Period 298-252 MYA Named for the city of Per’m in the Russian Ural Mountains by Roderick Murchison Assembly of Pangaea with large continental desert Modern terrestrial vertebrate groups became dominant Largest extinction event of the Phanerozoic at end of the Permian –most life extinguished

Causes of the end Permian extinction Volcanism Methane hydrate release Anoxia Hydrogen sulfide release Influence of Pangaea