GEOLOGICAL TIME SCALE (mya: million years ago)
 Eon Era Sub-era Period Epoch mya First Appereances
Phanerozoic Cenozoic Quaternary   Holocene .011
Pleistocene 1.64
Tertiary Neogene Pliocene 5.2 hominids
Miocene 23
Paleogene Eocene 35
Oligocene 56 grasses
Paleocene 65 primates
Mesozoic   Cretaceous   145 placental mammals
Jurassic   208 birds and bony fishes
Triassic   245 early mammals and dinousaurs
Paleozoic Permian   290  
Missisippian   323 conifers and winged insects
Pennsylvanian   362  
Devonian   408 sharks
Silurian   439 land plants
Ordovician   510 ammonoids
Cambrian   570 vertebrates, trilobites and many invertebrate groups
Pre- Cambrian  Age of the earth: 4.5 billion years
   mya shows the oldest boundary of the Epoch or Period