6.2 Geological time scale

. Geological time scale The duration of the earth’s history has been divided into eras that include the Paleozoic, Mesozoic, and Cenozoic. Recent eras are further divided into periods, which are split into epochs. The geological time scale with the duration of the eras and periods with the dominant forms of life is shown in Table . . The Paleozoic era is characterized by abundance of fossils of marine invertebrates. Towards the later half, other vertebrates (marine and terrestrial) except birds and mammals XII Std Zoology Chapter XII Std Zoology Chapter Evolution ERA YEARS IN MILLION PERIOD EPOCH FAUNA FLORA Cenozoic Quaternary Recent (Holocene) Age of Mammals Angiosperms Monocotyledons Pleistocene Age of Human beings Age of Angiosperms - Dicotyledons Tertiary Pliocene Human evolution Miocene Mammals and birds Oligocene Eocene Paleocene Mesozoic Cretaceous (Golden age of Reptiles) Rise of Dinosaurs Sphenopsides, Ginkgos, Gnetales, (Dicotyledons) Jurassic Herbaceous lycopods, Ferns, Conifers, Cycads Triassic Paleozoic Permian Mammal like reptiles Arborescent lycopods Carboniferous Pennsylvanian Earliest reptiles Seed ferns and Bryophytes Mississippian Earliest Amphibians and abundant Echinoderms Devonian Age of fishes Progymnosperms Silurian Earliest fishes and land invertebrates Zosterophyllum Ordovician Dominance of invertebrates Appearance of first land plants Cambrian Fossil invertebrates Origin of algae Precambrian Upper Multicellular organisms Middle Appearance of eukaryotes Lower Planktons prokaryotes Table . Geological Time Scale appeared. The six periods of Paleozoic era in order from oldest to the youngest are Cambrian (Age of invertebrates), Ordovician (fresh water fishes, Ostracoderms, various types of Molluscs), Silurian (origin of fishes), Devonian (Age of fishes, many types of fishes such as lung fishes, lobe finned fishes and ray finned fishes), Mississippian (earliest amphibians, Echinoderms), Pennsylvanian (earliest reptiles), Permian (mammal like reptiles). Mesozoic era (dominance of reptiles) called the Golden age of reptiles , is divided into three periods namely, Triassic (origin of egg laying mammals), XII Std Zoology Chapter XII Std Zoology Chapter Evolution viruses. Two major