GEOLOGIC TIME
EON	ERA	PERIODS AND SYSTEMS	EPOCHS AND SERIES	BEGINNING OF INTERVAL*	BIOLOGICAL FORMS
Phanerozoic	Cenozoic	Quaternary	Holocene Pleistocene	0.01 1.6	Earliest humans
		Tertiary	Pliocene Miocene Oligocene Eocene Paleocene	5 24 37 58 65	Earliest hominids Earliest grasses Earliest large mammals
	Cretaceous-Tertiary boundary (65 million years ago): extinction of dinosaurs
	Mesozoic	Cretaceous	Upper Lower	98 144	Earliest flowering plants; dinosaurs in ascendance
		Jurassic Triassic		208 245	Earliest birds & mammals Age of Dinosaurs begins
	Paleozoic	Permian Carboniferous Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian		286 320 360 408 438 505 570	Earliest reptiles Earliest winged insects Earliest vascular plants (as ferns & mosses) & amphibians Earliest land plants & insects Earliest corals Earliest fish
Proterozoic	Precambrian			2500	Earliest colonial algae & soft-bodied invertebrates
Archean				4000	Life appears; earliest algae & primitive bacteria

*In millions of years before the present