Principal divisions of geologic time + 
Dura- 
Era Period Epoch Characteristic life tion,» 
ss Recent. “‘Age of man.’”” Animals and plants of 
Quaternary. Pleistocene (great modern types. 
ice 
Cenozoic (recent age). 60 
life). Pliocene. 
ifiocene. “Age of ape peace nga first 
Tertiary. Oligocene —- of m: Rise and devel: 
Moses: ment of highest ¢ orders of plants, 
‘Age ofreptiles.’’ Rise and culmination 
Cretaceous. (*) of huge land reptiles (dinosaurs), of 
shellfish with complexly itioned 
coiled shells (ammonites), and of great 
Mesozoic (inter- (4 flying reptiles. First appearance of | 120 
mediate life). Jurassic, birds and pligoe ee (in Jurassic); of 
palmlike plants 
©) plan Se and of ris : 
; ¢ an _— Ww . are 
Triassic. ood trees (in sarnchoas S). 
“Age of amphibians.” of 
pee ater slg Ae en rev gs ‘ants of 
ve 
Permian. flowering oe. pe aaa o wai 
Carboniferous. | Pennsylvanian. g trees. Beginnings of back- | 120 - 
Mississippian. boned land animals (land vertebrates). lee 
sects. Animals with nautiluslike , 
Louse so aay (ammonites) and sharks 
“Age of fishes.”” Shellfish (mollusks) 
Devonian. (°) also abundant. Rise of amphibians | 90 a 
and land plants. ain 
pine faces viene ean = tilus 
es y nau 
sk ag aoe OE (cephalopods). Rise and 
Silurian. (©) of the : 30 om 
known as sea lilies (crinoids) and of 
giant scorpionlike crustaceans ( 
ape ). Hise of fishes and of: 
Ordovician (G) 90 
tes. niet trace of insect life. 
Trilobites and oe en : 
2 © acteristic weeds (algae 
Cambrian. ad abundant. No trace of land _ (algae) 60 
found, 
os <8 BM an - Ai a ge 
Proterozoic (pri- | “!eonkian. ; —— ~~ 
mordial life). 2 ee 
Archean. Crystalline rocks. | No fossils found. 
«The record consists mainly of sedimentary beds (beds deposited - oe Over large areas 
long pei of uplift and erosion intervened between See ete ee mnonition, aia pip hape ends wave 
deposition in any area produces there what geologists term an unconformity. Tlany oftie pitas 
por sina a” ag ge aed heer ti unconformities; that is, the dividing lines in the table represent local or x 
widespread oe -_ “tthe serie. 
Ages interpolated from H olmes, geo Eart wets k, Harpe B 1927. 
¢ Epoch names omitted; in less common use than those gi had = oe 
_ Notz.—Total estimated age of earth, 1,800+ million years, 
i 4 
