Principat Divisions oF GEeoLocic TIME.4 
[A glossary of geologic terms is given on pp. 199-203.] 
Duration, accord- 
Era. Period. Epoch. Characteristic life. ing be various 
estimates, 
“ ; Millions of years. 
ecent. 
Pleistocene | “Age of man.’? Animals and plants of 
Quaternary. re modem types. ‘ 
Cenozoic (re- we ASS 
cent life). § |__| 1to5. 
Pliocene 
= ; “‘Ageofmammals.”’ Possible first appear- 
Tertiary. 2 sexi fe of man. Rise and spain of 
8 aa highest orders of plants. 
“ Age of reptiles.” Rise and culmination 
Cretaceous. (*) f huge land reptiles ( ), of shell- 
fish with complexly partitioned coiled 
Mesozoic (in- ghee ag ste poe: and of sd be 
termediate Jurassic. () pe gh 2 ibe ig a — . ie) | 4 to 10. 
)- order of palmlike plants (in riassic); 
Mich ST tard wead eee 
Triassic. @) Ls 
i ¥ « Age of amphib: Dominance 
mosses = igeopods) ane terre of otal 
and fe: ive Roweriné 
Carbonifer- | Pennsylva- lants and earliest con 
ous, : backboned | a Sahmals 
(land ve fore tes). —— 
sarees tag with nautilus-like coile beg she ls (am 
Mississip-| ites) and sharks abundan 
pian. 
> “Age of fishes.” Shellfish (mollusks) also 
Devonian. (®) ee ag Rise of amphibians and land 
pl 
Paleozoic Shell-forming sea animals dominan 
(old life). cially those related to the nautilus toot 
y alopods). Rise and culmination of the 
Silurian. (>) marine animals sometimes mn sea | 17 to 25. 
lilies (crinoids) and of giant scorpion- 
like crustaceans Ketan al Rise 0: 
fishes and of reef-building corals. 
Shell-forming sea animals, espe 
anode = ie ts mre Bari 
Ordovician. (®) — dant, Culmina’ oo of the es 
First f trace of insect life. 
Trilobites and Deneitopads ie 
Cambrian. () teristic animals. Seaweeds (aig) abun ae 
dant. No trace of land 
. First life rang has left distinct record. 
Algonkian. (>) Crustaceans, brachiopods, and seaweeds. 
Proterozoic 
a oe ordi: T — 
sf Archean. ba sae No fossils found. 50+. 
a The geologic record consists mainly of sedimentary beds—beds deposited in water. Over large areas) 
a Log of uplift and erosion intervenod t between _— of comiormity. Shad vg in ro, = e 
sition in any area produces there w! geologists te an unconformi ogc d ra) time os 
shown above got > aye by such uneoniiomteee tat is, ; the dividing lines in the table represent Ag ee ea 
or ¥ or depressions of the earth’s surface. : 
bE common use than those given, 
