Geologic Time and Earth’s

Biological History
G E O G C I M
S A L

It is a record of the major events and diversity

of life forms present in Earth’s history.
 TRUE OR FALSE

The Geologic Time Scale is divided into four

different time units which are of the same
length.
 PERIOD, EON, EPOCH, ERA

Arrange the following in order of smallest to

largest.
P H N R O I O

The present eon

Eons:
Precambrian: Earliest span of time
Phanerozoic: Everything since

Eras:
Periods:
Paleozoic
Cambrian
Mesozoic
Ordovician
Cenozoic
Silurian
Paleozoic
“Age of
Devonian
Invertebrates” Carboniferous
(Missipp. & Pennsylvanian)
Epochs:
Permian
Paleocene
Triassic
Mesozoic Eocene
Jurassic
“Age of Reptiles” Oligocene
Cretaceous
Paleogene
Cenozoic Miocene
Neogene
“Age of Pliocene
Mammals” Quaternary
Pleistocene
Holocene

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 The Earth Through Time
The Proterozoic:
 No life possible as the Earth initially forms 4.6
billion years ago.
 Simple, single-celled forms of life appear 3.8
billion years ago, becoming more complex and
successful over the next 3 billion years:
Prokaryotes then Eukaryotes
 Cyanobacteria begins producing free oxygen
(photosynthesis)

Cambrian:
 Explosion of life
 All existing phyla come into being at this time
 Life forms in warm seas as oxygen levels rise
enough to support life
 Dominant animals: Marine invertebrates
(trilobites and brachiopods)

PaleoMaps used with permission from Christopher Scotese and are under 7
copyright of C.R. Scotese, 2002

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Ordovician:
 The 1st animals with bones appear, though
dominant animals are still trilobites, brachiopods
and corals
A very cold time in Earth’s history: there was a
great extinction due to ice caps

Silurian:
 First land plants appear and land animals follow
Coral reefs expand and land plants begin to
colonize barren land.
 First millipede fossils and sea scorpions
(Euryptides) found in this period

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Table of Contents 20
Devonian (Age of the Fish)
 Pre-Pangea forms. Dominant animal:
fish
Hardwoods began to grow.
 Amphibians, evergreens and ferns
appear

PaleoMaps used with permission from Christopher Scotese and are under
Mississippian: copyright of C.R. Scotese, 2002
 First seed plants appear

Pennsylvanian:
Ice covers the southern
hemisphere and coal swamps
formed along equator.
 Lizards and winged insects first
appear.

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Table of Contents 21
Permian:
 Last period of the Paleozoic
 Pangea forms. Reptiles spread
across continents.
90% of Earth’s species become
extinct due to volcanism This marks
the end of trilobites, ammonoids,
blastoids, and most fish.

Triassic:
 First dinosaurs appear
 First mammals- small rodents appear
 Life and fauna re-diversify
 Rocky Mountains form.
 First turtle fossil from this period
 Pangea breaks apart

PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002

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Jurassic:
 Pangea still breaking apart
 Dinosaurs flourish “Golden age of
dinosaurs”
 First birds appear


Cretaceous:
 T-Rex develops
 First snakes and primates appear
 Deciduous trees and grasses
common
 First flowering plants
 Mass extinction marks the end of
the Mesozoic Era, with the demise
of dinoaurs and 25% of all marine
life.
PaleoMaps used with permission from Christopher Scotese and are under copyright of
C.R. Scotese, 2002 Table of Contents 11
Tertiary:
 First horses appear and tropical
plants dominate (Paleocene)
 Grasses spread and whales, rhinos,
elephants and other large mammals
develop. Sea level rises and
limestone deposits form in S.C.
(Eocene)
 Dogs, cats, and apes appear
(Oligocene)
 Horses, mastadons, camels, and
tigers roam free in S.C. (Miocene)
 Hominids develop and the Grand
Canyon forms (Pliocene)

Quaternary:
 Modern humans develop and ice
sheets are predominant- Ice age
(Pleistocene)
 Holocene Humans flourish
(Holocene)

PaleoMaps used with permission from Christopher Scotese and are under
copyright of C.R. Scotese, 2002
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