Spring 2015
8 th Grade
The geologic time scale is a record of the major events
and diversity of life forms present in Earth’s history.
 The geologic time scale began when Earth was
formed and goes on until the present.
 At the end of each era a mass extinction occurred,
many kinds of organisms died out, although there
were other extinctions going on during each
period of geologic time.
 Using the fossil record, paleontologists have
created an idea of the different types of common
organisms in each
geologic period.
Eras are subdivided into periods...periods are
subdivided into epochs.
Era
Period
Epoch
E + P = EP
Various models, diagrams, and pictures can be used to
illustrate the vastness of time involved in and to show
the diversity of life evident across geologic time.
Mesozoic Era
CretaceousFlowering Plants,
Major extinction of
Dinosaurs
Jurassic- Early
birds & Mammals,
abundant dinosaurs
Triassic- Lots of
Conifers, 1st Dinos, 1st
Mammals
Paleozoic
PermianMass Extinction of
marine animals
like trilobites
Devonian –
Early trees
SilurianEarly land plants
OrdovicianEarly Fish
Precambrian
ProterozicSingle→Multicellular
Organisms.
Archean–
Oldest fossils, bacteria
& sinlge celled
organisms
88% of the History of Earth
4.6 Billion Years Ago – 450 Million Years Ago
(Color in 27 wedges)
 Earth's first era of time.
 5 major events occurred during this era:
(1) the formation of the Sun and light
(2) the creation of the Earth
(3) the creation of the atmosphere through
volcanic out-gassing
(4) the creation of the oceans
(5) the creation of life
 Began with simple life forms such as bacteria and simple
algae.
 There was a rise of simple organisms such as jellyfish and
sea worms by the end of the era.
 Few fossils because the life forms were soft-bodied and had
no hard skeleton.
Geological Events:
 Earth Began
Biological Events:
 Bacteria Appear
 Soft-Bodied Multi-Cellular
Organisms Appear
Ancient Life
544 Million Years Ago – 244 Million Years Ago
(Color in 3 wedges)
Animal Life:
 Began with the early
invertebrates, such as
trilobites and brachiopods.
 Continued to develop early
vertebrate fish, arachnids
and insects.
 Later came the first
amphibians and near the
era’s end the reptiles
became dominant.
 Plant Life:
 Early land plants included
simple mosses, ferns, and
then cone-bearing plants.
 By the end of the era,
seed plants were common.
 The mass extinction that ended the era caused
most marine invertebrates as well as amphibians
to disappear.
Geological Events:
Biological Events:
 Shallow seas cover
• Great explosion of
invertebrates in the sea
(Trilobites appear)
• Land plants appear
• Insects and spiders
appear
• Age of fish begins
• First reptiles appear
• Trilobites become
extinct
much of the land
 Coral reefs develop
 Pangaea forms
 Appalachian
Mountains form
Middle Life
245 Million Years Ago – 65 Million Years Ago
(Color in 1 ½ wedges)
 Reptiles were the dominant animals
of this era, including the various
dinosaurs.
 Small mammals and birds also appeared.
 Toward the end of the era, flowering plants
appeared and the kinds of mammals increased.
 The mass extinction that ended the era caused the
dinosaurs to become extinct.
Geological Events:
 Hot, dry conditions dominate Pangaea
 Pangaea splits
 Widespread volcanic activity
Biological Events:
 Dinosaurs appear
 Largest dinosaurs thrive
 Dinosaurs become extinct
 Mammals, birds and flowering plants appear
Recent Life
65 million years ago - Today
(Color in a ½ wedge)
 New mammals appeared
while others became extinct.
 Mammals had to evolve to adapt
to different environments.
 The diversity of life forms
increased.
 Flowering plants became
most common.
 Humans are also part of the most recent period of this
era.
 Many mountain ranges formed
 ex. Alps in Europe, Himalayas in India & Rocky
Mountains in the USA
Geological Events:
 Rocky Mountains and Himalayas form
 Continental glaciers cover Antarctica
 Ice age ends
Biological Events:
 First grasses appear
 Mammals, flowering plants, and insects
dominate the land
 Humans appear