Principat Divisions oF GEoLocic TIME,@ 
[A glossary of gesloz g p. 182-185.] 
Duration, accord- 
Era. Period. Epoch. Characteristic life. ing to various 
estimates. 
Miilions ef years. 
Recent. ; 
“Age of man,’’ Animals and plants of 
Quaternary. | Osent modern types 
Iee Age). 
Cenozoic (re- 
cent life). ia ak 
Sapien “Ageofmammals.”’ Possible first appear- 
Tertiary. opr : ance of man. Rise and development of 
Song highest orders of plants. 
: ** Age of reptiles and ¢ 
Cretaceous. (0) line land tepilles ret oreo of shell. 
— with in sad Plage pare coiled 
35S 4 hells (ammonites), and of gZ 
Mesozoic (in- ea y ; 0 
; ptiles. First appearance @ J sinus 4 to 10. 
a Jurassic. (0) of birds and mammals; of cycads, | 
pee mi ee order of e plants Triassic) ; 
and of angiospermous fe b pre 
Triassic. (b) tere Fa a and dwood trees 
Permian. 
“Age ofamphibians.” Dominance of club 
(lycopods) and plants of horsetail 
Ponnevt and fern types. itive flowering 
Carbonifer- | * Sasy've- lants and earliest cone- tr 
ous. ipoas ginnings of backboned land animals 
| (land vertebrates). Insects. Animals 
: ; with nautilus-like coiled shells (ammon- 
Mississip- Pe) and sharks abundant. 
plan. 53 : 
: “ Age of fishes.” sihaltna Waaiwesi) aise | 
Devonian. (b) pet etd Rise of amphibians and land 
plan 
Paleozoic Shell-forming sea animals dominan 
(old life). cially those become to the nautilus (ceph- : 
alopods). _ and culminat f the 
Silurian. (b) — inown ae sea | 17 to 25. 
lilies (crinoids) ak 0 t scorpion- 
like crustaceans (e eid) —— of 
fishes and of reef-building coral 
Shell-forming sea animals, e ecially ceph- 
2 alopods and mollusk ike brachiopods, 
Ordovician. (b) abundant. Cu = he buglike 
marine crustacean: as trilobites. 
First trace of ingect — 
: Trilobites and brachio most ¢ 
Cambrian. (b) Soares (zt) abun: 
dan of land anima! 
Se SS REO OEE ENG 
Algonkian (b) First life that hc — distinet record. 
Proterozoic Crustaceans, brachiopods, and seaweeds. 
me 
Archean. | Crystalline | 17, fossils found. 50-4 
@ The geologic record consists consists mainly of sedimen beds —beds-deposited 
in water. areas 
ee : erosion intervened ‘een periods o: poo agg Pens such eee 
deposition y area epee be there what geologists term an unconformit a of a ae 
spe canta pew ppm ed such unconformities—that is, the dividing lines in t t local 
i to) 
"apes or depressions of the earth’s nes 
names omitted; in less common use than those given. 
Ir 
