PRINCIPAL DIvIsIons oF GEOLOGIC TIME.? 
Duration, accord- 
Era. Period. Epoch. Characteristic life. ing to various 
estimates. 
reser Millions of years. 
ecent. 
Pleistocene | ‘‘Age of man.” Animals and plants of 
Quaternary-| “(Great | modern types. 
io ( Ice Age). 
Cenozoic (re- 
cent life). 1to5. 
Pliocene. te ” 
: Miocene. eee of (eile. Possible first appear- 
Tertiary. ise and development of 
a hishest cee of plants. 
Cretaceous. b “Age of reptiles.” Rise and culmination 
~ < @) af ne res ea mena genom 
y part: coi 
— shells ( onites), and of erent flyin: 
Mesozoic (in- : tiles. First appearance of birds de 
termediate Jurassic. (6) — ier Faraasie): of 6 eads, an 4 to 10. 
* peal 2 palmlike plants (in Triassic 
haierpecisous plants, among 
es aa are palms and hardwood tree: 
Triassic. (>) (in Cretaceous). 
“‘Ageofamphibians.’”’ Dominance ofclub 
Periian. ego = ie “Primitive *fdowering 
Carbonifer- P enpp he lants an 
ous. Mississip- fore backboned land animals 
= th naztilgadilegapligd-ahelie tanmor- 
ites) and sharks abundant. 
fe: Age offishes.”’? Shellfish (mollusks) also 
Devonian. (2) undant. Rise ofamphibians and land 
Paleozoic Shell-forming sea animals dominant, espe- 
(old life). cially those related tothe naenititis (ceph- 
salap eds). Ri culmin 1 of the 
Silurian. (>) e animals sometimes ‘po mas sea | 17 to 25. 
lilies (crinoids) and of giant scorpion- 
like crustaceans (eurypterids). Rise of 
fishes and of reef-building corals. 
Shell-forming sea: ceph- 
ae alopods and goo gee em id 
Ordovician. (>) abun pret sige Culmination of by bupiks 
as trilobit 
Fuect trace of insect life. 
Trilobites and Picbiopcas wm 
Cambrian. (>) teristic animals. Seaweeds algae) abun- ey a 
dant. Notrace ofland animals foun 
i ee life that has left distinct record. 
__ | Algonkian. *) rustaceans, brachiopods, and seaweeds. 
Prot erozoic 
a 
: ‘Avelionn: = No fossils found. 50+. 
deposition! = = area Ley agro there what geologists t an unconformi 
“ y such une onformities—that i is, the dividing lines in the table re veprepett local 
an. 
ir 
he geologic record consists mainly of sedimentary beds—beds deposited in water. Over large areas 
ste setleae of uplift and erosion. reervonat between —— of deposition. ptt such Peete ption in 
tree depclidtens ol the cirtts ta: nen 
ao omitted; in less common use than those given. 
of the tim 
ivisions 
