geologic timescale

divisions of the timescale

eons, eras, periods, epochs

Four eons (oldest to youngest)

Hadean, Archean, Proterozoic, Phanerozoic

three eons of the precambrian period

hadean, archean, proterozoic

three eras of the phanerozoic eon (oldest to youngest)

Paleozoic, mesozoic, cenozoic

paleozoic era

marine invertebrates; fishes; age of amphibians

eight periods of the paleozoic era

Cambrian, ordovician, silurian, Devonian, Mississippian, Pennsylvanian, carboniferous, permian

mesozoic era

age of reptiles

three periods of the mesozoic era (oldest to youngest)

triassic, jurassic, cretaceous

cenozoic era

age of mammals

four periods of the cenozoic era (oldest to youngest)

paleogene, tertiary, neogene, quaternary

three epochs of the paleogene period (oldest to youngest)

paleocene, eocene, oligocene

two epochs of the neogene period (oldest to youngest)

miocene, pliocene

two epochs of the quaternary period (oldest to youngest)

pleistocene and holocene