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|
I-5
Geologic Time Chart
Webster's
New World Dictionary 585
| MAIN
DIVISIONS OF GEOLOGIC TIME |
PRINCIPAL
PHYSICAL AND BIOLOGICAL FEATURES
|
| ERAS |
PERIODS
or SYSTEMS
Epochs
or Series
|
|
|
Quarternary
|
Recent
12,000* |
Glaciers
restricted to Antartica and Greenland; extinction of giant mamals;
development and spread of modern human culture. |
| Pleistocene
600,000 |
Great
glaciers covered much of N America & NW Europe; volcanoes
along W coast of U.S.; many giant mammals; appearance of modern
humans late in Pleistocene. |
|
Tertiary
|
Pliocene
10,000,000 |
W
North America uplifted; much modernization of mammals; first possible
apelike humans appeared in Africa. |
| Miocene
25,000,000 |
Renewed
uplift of Rockies & other mountains;** great lava flows in
W U.S.; mammals began to acquire modern characters; dogs, modern
type horses, manlike apes appeared. |
| Oligocene
35,000,000 |
Many
older types of mammals became extinct; mastodons, first monkeys,
and apes appeared. |
| Eocene
55,000,000 |
Mountains
raised in Rockies, Andes, Alps, & Himalayas; continued expansion
of early mammals; primitive horses appeared. |
| Paleocene
65,000,000 |
Great
development of primitive mammals. |
|
|
Cretaceous
135,000,000
|
Rocky
Mountains began to rise; most plants, invertebrate animals, fishes,
and birds of modern types; dinosaurs reached maximum development
& then became extinct; mammals small and very primitive. |
|
Jurassic
180,000,000
|
Sierra
Nevada Mountains uplifted; conifers & cycads dominant among
plants; primitive birds appeared. |
|
Triassic
230,000,000
|
Lava
flows in E North America; ferns & cycads cominant among plants;
modern corals appeared & some insects of modern types; great
expansion of reptiles including earliest dinosaurs. |
|
|
Permian
280,000,000
|
Final
folding of Appalachians & central Eurpoean ranges; great glaciers
in S Hemisphere & reefs in warm northern seas; trees of coal
forests declined; ferns abundant; conifers present; first cycads
& ammonites appeared; trilobites became extinct; reptiles
surpassed amphibians. |
|
|
Pennsylvanian
310,000,000
|
Mountains
grew along E Coast of North America & in central Europe; great
coal swamp forests flourished in N Hemisphere; seed-bearing ferns
abundant; cockroaches & first reptiles appeared. |
|
Mississippian
345,000,000
|
Land
plants became diversified, including many ancient kinds of trees;
crinoids achieved greatest develpoment; sharks of relatively modern
types appeared; land animals little known. |
|
Devonian
405,000,000
|
Mountains
raised in New England; land plants evolved rapidly; large trees
appeared; branchiopods reached maximum development; many kinds
of primitive fishes; first sharks, insects, & amphibians appeared.
|
|
Silurian
425,000,000
|
Great
mountains formed in NW Europe; first small land plants appeared;
coral built reefs in far northern seas; shelled cephalopods abundant;
tilobites began to decline; first jawed fish appeared. |
|
Ordovician
500,000,000
|
Mountains
elevated in New England; volcanoes along Atlantic Coast; much
limestone deposited in shallow seas; great expansion among marine
invertebrate animals; all major groups present; first primitive
jawless fish appeared. |
|
Cambrian
600,000,000
|
Shallow
seas covered parts of continents; first abundant record of marine
life, esp. trilobites & branchiopods; other fossils rare. |
|
|
Late
Precambrian (Algonkian)***
2,000,000,000
|
Metamorphosed
sedimentary rocks, lava flows, granite; history complex &
obscure; first evidence of life; calcareous algae & invertebrates. |
|
Early
Precambrian (Archean)***
4,500,000,000
|
Crust
formed on molten earth; crystalline rocks much disturbed; history
unknown. |
*Figures
indicate approx. number of years since beginning of each division. **Mountanin
uplifts generally began near the end of a division. ***Regarded as separate
eras.
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Schematic I-4
