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

Cambrian 540 - 510 million years ago Life Dominant life includes: Trilobites, Brachiopods During this time period life evolves very quickly and into many complex organisms. Almost every major group of animals appear in this very short time span. This rapid diversification is known as "The Cambrian Explosion." During this time, the oxygen that is being produced by photosynthesis begins mixing with the oceans, which may be responsible for the "explosion" of life. Climate The Cambrian is "sandwiched" between major ice ages at its beginning and end, however the climate was primarily mild with little significant ice. Geology The main rock types/ deposits in PA are limestone, dolomite, and quartzite.