ERA PERIOD AGE (of start) Cenozoic Quaternary 1.6 my Tertiary 65 my Mesozoic Cretaceous 140 my Jurassic 205 my Triassic 250 my Paleozoic Permian 290 my Carboniferous 355 my Devonian 410 my Silurian 438 my Ordovician 510 my Cambrian 540 my

Silurian 438 - 410 million years ago Life Dominant life includes: Corals, fish The first known freshwater fish and jawed fish appeared during this time. Climate Climate becomes more stable during the Ordovician, as opposed to previously when there were extreme climatic fluctuations. Geology The main rock types/ deposits in PA are limestone, sandstone, and conglomerate.