Earth Science 13.2A Paleozoic Era : Life explodes
Paleozoic Era :
Life Explodes
Paleozoic Era
The Paleozoic Era followed the
Precambrian period, running from
542 million years ago to 251 million
years ago.
Throughout the Paleozoic era,
there were major developments in
the evolution of life. Many of these
developments occurred in response
to environmental changes.
Each species is fitted to survive in
a particular type of environment. If
the environment changes too much;
the species must evolve or die off.
Trilobite fossil from early
Paleozoic era
Paleozoic Era
Environmental changes that have
affected the course of evolution on
Earth include
 The formation and breakup of
 Mountain building
 Volcanic activity
 Changes in climate
 Changes in sea level
Such changes have affected
evolution throughout geological
Rapid change can lead to mass
extinction; the extinction of many
groups in a short amount of time.
Fossil records show that with each
mass extinction; life rebounded
back as new species evolved.
Trilobite fossil from early
Paleozoic era
Paleozoic Era
The Paleozoic Era divides up into 6
time intervals called periods
 Cambrian period (542 – 488
 Ordovician period (488- 444)
 Silurian period (444 – 416)
 Devonian ( 416 – 359)
 Carboniferous period (359 – 299)
 Permian (299 – 251)
Many firsts in the history of
evolution occurred during this era;
from the first organisms with
shells up to the first birds and
flowering plants.
Trilobite fossil from early
Paleozoic era
Paleozoic Era: Cambrian period
Cambrian Period: (542 – 488)
 As during the Precambrian era, life
in the early Paleozoic was found
only in the seas.
But the Cambrian period (542488) brought dramatic changes to
Many new groups of organisms
evolved in a relatively short time in
an event geologists refer to as the
“Cambrian explosion”.
Paleozoic Era: Cambrian period
Cambrian Earth:
Geologic developments contributed
to the Cambrian explosion. The
breakup of the supercontinent
Rodinia formed many pieces of
New environments formed in the
shallow seas between these pieces,
some of which lay near the equator.
Earth continued to warm after an
ice age that had chilled the planet
in the late Precambrian. This
warming trend may have been a
factor in the evolution of new living
Paleozoic Era: Cambrian period
Cambrian Life:
 As a result of the Cambrian
explosion, the number of different
kinds of organisms increased
greatly in only 15 million years.
Cambrian organisms are well know
from the Burgess shale, a fossilrich formation in the Canadian
Rockies. Most Burgess shale fossils
belong to several groups of
An invertebrate is an organism that
lacks a backbone. The Burgess
shale fossils also include early
ancestors of vertebrates,
organisms that did have backbones.
Paleozoic Era: Cambrian period
Cambrian Life:
 Cambrian animals were the first to
evolve hard parts such as shells.
 The shells of mollusks, such as
clams and snails, protected them
from dangers in their environments.
Shells also allowed body organs to
function in a more controlled
Animals called arthropods evolved
that had an external skeleton made
of a protein called chitin.
Modern day arthropods include
insects and crustaceans.
Paleozoic Era: Cambrian period
Cambrian Life:
One arthropod that developed early
in Cambrian life was the trilobite.
A trilobite’s exoskeleton allowed it
to burrow through soft mud in
search of food.
More than 600 types of these mud
burrowing scavengers evolved
worldwide during this era.
Geologists also found limestones
from the Cambrian period that
began as reefs in the oceans.
Cambrian reefs were made up of
the remains of sponges or mats of
material produced by
Paleozoic Era: Ordovician period
Ordovician period: (488-444) Major
During the Ordovician period, more
complex communities of organisms
developed in the oceans.
The first land dwelling plants
This period ended with a mass
Paleozoic Era: Ordovician period
Ordovician Earth:
Plate movements pushed the huge
landmass of Gonwanda south during
the Ordivician.
Part of five of today’s continents
are made up of Gonwanda: South
America, Africa, Australia,
Antarctica, and parts of Asia.
Collisions between landmasses near
the equator led to mountain building
in what is now eastern North
Paleozoic Era: Ordovician period
Ordovician Ocean Life:
During the Ordovicain period, the
diversity of organisms living in the
ocean increased. For example, reefbuilding invertebrates called
bryozoans evolved, along with early
Brachiopod fossils
Trilobites continued to be
abundant, and shelled organisms
called brachiopods became even
more common.
Vertebrates became more common
as jawless fishes evolved. Jawless
fishes had a bony, external
covering and are the ancestors of
today’s modern fishes.
Ordivician jawless fish
Paleozoic Era: Ordovician period
Ordovician Plant Life:
Another major development in the
Ordovician period was the
development of land plants.
These first plants resembled small,
primitive plants such as liverworts.
They lived in moist areas and
reproduced through spores, not
As plants multiplied on land, they
added oxygen to the atmosphere.
Geologists think that an ice age
caused a mass extinction at the end
of the Ordovician period. Volcanic
eruptions may have contributed to
this event.
Modern day liverworts
Paleozoic Era: Silurian period
Silurian Earth: (444-416) The Seas
During this time, several factors
caused sea levels to rise, flooding
low lying parts of continents.
Large barrier reefs formed in
these shallow seas.
The reefs restricted circulation
between shallow marine basins and
the open ocean.
Water in these basins evaporated,
depositing large quantities of rock
salt and gypsum.
Silurian Period
Paleozoic Era: Silurian period
Silurian Earth: Life
In the oceans, reef building corals
developed. Jawless fish survived,
developing thick armored plates.
The first jawed fish evolved during
this period.
Other ocean organisms during this
period include arthropods called
On land, small plants similar to
mosses spread over moist lowland
areas. The first vascular plants
vascular plant
Paleozoic Era: Silurian period
Silurian Earth: Plant Life
The stem of a vascular plant
contains thin tubes that carry
liquids within the plant.
These early plants were leafless
spikes about the size of your index
There is no evidence from trace
fossils that arthropods began to
adapt to life on land during the
Silurian period.
The Rhyniophyta comprise
the oldest known division
of vascular plants during
the Silurian period of 400
million years ago. The
shoot is leafless and
dichotomously branched in
the genus Rhynia.
Cooksonia is the oldest
known vascular plant.

Earth Science 13.2 Paleozoic Era : Life explodes