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THE EARTH THROUGH TIME
TENTH EDITION
H A R O L D L. L E V I N
© 2013 JOHN WILEY & SONS, INC. ALL RIGHTS RESERVED.
1
CHAPTER 9
Proterozoic: Dawn of a More Modern World
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PROTEROZOIC EON

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2.5 billion years to 542 million years ago
Comprises 42% of Earth history
Divided into three eras:
 Paleoproterozoic Era (2.5 - 1.6 by ago)
 Mesoproterozoic Era (1.6 to 1.0 by ago)
 Neoproterozoic Era (1.0 by ago to the
beginning of the Paleozoic, 542 my ago)
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THE BEGINNING OF PROTEROZOIC
MARKS THE BEGINNING OF:
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More modern style of plate tectonics
More modern style of sedimentation
More modern global climate with glaciations
Establishment of the beginnings of an oxygen-rich
atmosphere
Emergence of eukaryotes
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PRECAMBRIAN PROVINCES IN
NORTH AMERICA
Precambrian provinces were welded (or
sutured) together to form a large continent
called Laurentia during Early Proterozoic.
 Suturing occurred along mountain belts
or orogens.
 Provinces were assembled by about 1.7
b.y. ago.
 Laurentia continued to grow by accretion
throughout Proterozoic.
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PROTEROZOIC SEDIMENTATION
Sedimentation on and around the craton
consisted of shallow water clastic and carbonate
sediments deposited on broad continental shelves
and in epicontinental seas.
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PROTEROZOIC CLIMATE AND TECTONICS

Proterozoic glaciations occurred during:
 Paleoproterozoic, about 2.4–2.3 b.y. ago
(Huronian glaciation)
 Neoproterozoic, 850–600 m.y. ago (Varangian
glaciation)
During Late Proterozoic, the continents became
assembled into a supercontinent called Rodinia.
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OVERVIEW OF THE PRECAMBRIAN
FIGURE 9-31 Correlation of major events in the biosphere, lithosphere, and atmosphere.
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OVERVIEW OF
PROTEROZOIC
EVENTS
FIGURE 9-1 Pathway
through the Proterozoic,
depicting major geologic
events.
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PALEOPROTEROZOIC ERA
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The oldest part of Proterozoic
Ranges from about 2.5 b.y. to 1.6 b.y.
Covers 900 million years
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MAJOR EVENTS OF THE
PALEOPROTEROZOIC
1.
2.
3.
4.
5.
Active plate tectonics
Major mountain building on all major continents
Earth's first glaciation
Widespread volcanism (continental flood basalts)
Rise in atmospheric oxygen (great oxidation event)
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MAJOR EVENTS OF THE
PALEOPROTEROZOIC
6.
7.
Accumulation of high concentrations of organic
matter in sediments (Shunga event) 2000 m.y.
ago, and generation of petroleum
Oldest known phosphorites and phosphate
concretions
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OROGENIC BELTS
Orogenic belts developed around margins of the
Archean provinces.
 Wopmay belt in NW Canada
 Trans-Hudson belt, SW of Hudson Bay
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WOPMAY OROGENIC BELT CONTAINS
EVIDENCE OF:
1.
2.
3.
Rifting and opening of an ocean basin (with
normal faults, continental sediments, and lava
flows)
Sedimentation along new continental margins
(with shallow marine quartz sandstones and
carbonate deposition)
Closure of the ocean basin (with deep water
clastics overlain by deltaic and fluvial sands),
followed by folding and faulting.
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WILSON CYCLE
This sequence of events in the Wopmay orogenic belt
is called a Wilson Cycle, and is a result of plate
tectonics.
1.
Rifting and opening of an ocean basin
2.
Sedimentation along new continental margins
3.
Closure of the ocean basin
The sequence of events in the Wopmay belt is similar
to that in Paleozoic rocks of the Appalachians.
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TRANS-HUDSON OROGENIC BELT
Trans-Hudson belt contains the sedimentary record of
a Wilson Cycle, with evidence of:
1. Rifting
2. Opening of an ocean basin
3. Deposition of sediment
4. Closure of the ocean basin along a subduction
zone, associated with folding, metamorphism, and
igneous intrusions.
This closure welded the Superior province to the
Hearne and Wyoming provinces to the west.
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PALEOPROTEROZOIC GLACIATION—
EARTH'S FIRST ICE AGE?
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A Paleoproterozoic ice age is recorded in rocks north
of Lake Huron in southern Canada (called the
Huronian glaciation).
Gowganda Formation.
Age of Huronian glaciation = 2450–2220 m.y.
Apparent rapid onset of global glaciations from what
had been relatively stable climatic conditions.
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EVIDENCE FOR GLACIATION INCLUDES:
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Mudstones with laminations or varves: fine
laminations indicating seasonal deposition in lakes
adjacent to ice sheets.
Glacial dropstones (dropped from melting icebergs)
in varved sedimentary rocks.
Tillites or glacial diamictites (poorly sorted
conglomerates of glacial debris).
Scratched and faceted cobbles and boulders in
tillite, due to abrasion as ice moved.
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WIDESPREAD GLACIATION
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Age of global glaciations = 2.6–2.1 b.y. ago (2600–
2100 m.y.).
Widespread glaciation at this time as indicated by
glacial deposits found in:
 Europe
 Southern
Africa
 India
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BANDED IRON FORMATIONS AND
PROKARYOTE FOSSILS
Extensive banded iron
formations (BIF's) on the
western shores of Lake
Superior, indicate that
photosynthesis was
occurring and oxygen
was being produced.
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BANDED IRON FORMATIONS AND
PROKARYOTE FOSSILS

Animikie Group.
 Some BIF deposits are >1000 m thick, and
extend over 100 km.

The Gunflint Chert, within the BIF sequence,
contains fossil remains of prokaryotic
organisms, including cyanobacteria.
Age = 1.9 b.y.
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LABRADOR TROUGH
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East of the Superior province are rocks deposited
on a continental shelf, slope, and rise.
Rocks are similar to those of the Wopmay orogenic
belt.
These rocks were folded, metamorphosed, and
thrust-faulted during the Hudsonian orogeny, which
separates the Paleoproterozoic from the
Mesoproterozoic.
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HIGHLIGHTS OF THE MESOPROTEROZOIC
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The Mesoproterozoic (or middle Proterozoic) ranges
from about 1.6 b.y.–1.0 b.y.
The Midcontinent rift, an abandoned oceanic rift in
the Lake Superior region with massive basaltic lava
flows
Copper mineralization in the Lake Superior region
Continental collisions producing the Grenville
orogeny in eastern North America
The assembly of continents to form the
supercontinent, Rodinia.
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MIDCONTINENT RIFT AND THE
KEWEENAWAN SEQUENCE
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Midcontinent rift extends southward from Lake
Superior region.
Overlies Archean crystalline basement rocks and
Paleoproterozoic Animikian
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MIDCONTINENT RIFT AND THE
KEWEENAWAN SEQUENCE
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Large volumes of basaltic rock indicate presence of
an abandoned rift zone called the Midcontinent rift.
This was the first stage of a Wilson Cycle.
Rift developed 1.2 b.y.–1.0 b.y. ago.
Extended from Lake Superior to Kansas.
Rifting ceased before the rift reached the edge of
the craton, or the eastern U.S. would have drifted
away from the rest of North America.
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MIDCONTINENT RIFT AND THE
KEWEENAWAN SEQUENCE
The Keweenawan Sequence consists of:
 Clean quartz sandstones
 Arkoses
 Conglomerates
 Basaltic lava flows more than 25,000 ft thick
(nearly 5 mi) with native copper
 Basaltic rock beneath the surface crystallized as
the Duluth Gabbro, 8 mi thick and 100 mi wide.
 Native copper fills vesicles (gas bubbles) in the
Keweenawan basalt, and joints and pore spaces in
associated conglomerates.
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GRENVILLE PROVINCE AND
GRENVILLE OROGENY
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Grenville rocks were originally sandstones and
carbonate rocks.
Grenville Province was the last Precambrian
province to experience a major orogeny.
Grenville orogeny = 1.2 b.y.–1.0 b.y. ago
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GRENVILLE PROVINCE AND
GRENVILLE OROGENY
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Orogeny occurred when Eastern North America
(Laurentia) collided with western South America
(Amazonia).
Orogeny was associated with formation of the
supercontinent, Rodinia.
Later, during Paleozoic, Grenville rocks were
metamorphosed and intruded during the three
orogenies involved in the building of the
Appalachians.
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THE SUPERCONTINENT, RODINIA
The supercontinent,
Rodinia, as it appeared
about 1.1 b.y. ago.
The reddish band down
the center of the globe is
the location of
continental collisions and
orogeny, including the
Grenville orogeny.
FIGURE 9-10 The supercontinent Rodinia as
it appeared about 1100 million years ago.
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THE SUPERCONTINENT, RODINIA
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Rodinia formed as the continents collided during
the Grenville Orogeny.
Rodinia persisted as a supercontinent for about
350 million years.
It was surrounded by an ocean called Mirovia.
Rodinia began to rift and break up about 750
million years ago, forming the proto-Pacific
Ocean, Panthalassa, along the western side of
North America.
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RIFTING IN RODINIA
An early failed attempt at rifting began in eastern
North America about 760 m.y. ago, with the
deposition of sediments of the Mount Rogers
Formation in a fault-bounded rift valley.
Felsic and mafic volcanic rocks are interlayered with
the sedimentary rocks of the Mount Rogers
Formation.
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NEOPROTEROZOIC ERA
The Neoproterozoic (or "new" Proterozoic) ranges
from about 1.0 b.y. to 0.542 b.y. (542 m.y.).
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HIGHLIGHTS OF THE NEOPROTEROZOIC
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Extensive continental glaciations
Sediments deposited in basins and shelf areas
along the eastern edge of the North American
craton.
Most of these rocks were deformed during
Paleozoic orogenies.
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GLACIAL DEPOSITS—NEOPROTEROZOIC
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Glacial deposits formed roughly 635–850 m.y. ago.
Evidence for glaciation:
 Glacial striations (scratched and grooved pebbles
and boulders)
 Tillites (lithified, unsorted conglomerates and
boulder beds) found nearly worldwide
 Glacial dropstones (chunks of rocks released from
melting icebergs)
 Varved clays from glacial lakes
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GLACIAL DEPOSITS NEOPROTEROZOIC
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Varangian glaciation (named after an area in
Norway).
Ice age lasted about 240 m.y.
Glacial related deposits are widespread (even
in tropical latitudes).
 Cryogenian period
 It has been proposed that the entire
planet was cover in ice "snowball Earth"
or that ice did not extend beyond the mid
latitudes “slushball Earth”
Glaciation was followed by tropical condition
as evidence by the deposition of carbonates
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FIGURE 9-11 Earth has seen several major episodes of
widespread continental glaciation (orange).
PLATE TECTONICS AND GLACIATION
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Plate tectonics may have had a role in cooling the
planet.
Continents were located around the equator
about 600 to 700 m.y. ago.
No tropical ocean.
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PLATE TECTONICS AND GLACIATION
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Heat lost by reflection from the rocks on the surface
of the continents may have caused global cooling.
(Land plants had not yet appeared.)
As continental glaciers and ice caps formed,
reflectivity of snow and ice caused further
temperature decrease.
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ATMOSPHERIC GASES AND GLACIATION

Glaciation was associated with:
 Decrease
in CO2 and
 Increase in O2.
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CO2 causes the greenhouse effect and global
warming. Decrease in CO2 may have caused
cooling.
Decrease in CO2 was probably caused by increase
in the number of photosynthetic organisms
(cyanobacteria, stromatolites).
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LIMESTONES AND GLACIATIONS
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Limestones are associated with glacial deposits,
which is unusual, since limestones generally form in
warm seas, not cold ones.
Association of limestones with glacial deposits
suggests that times of photosynthesis and CO2
removal alternated with times of glaciation.
Limestones (made of CaCO3) are a storehouse of
CO2, which was removed from the atmosphere.
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LIMESTONES AND GLACIATIONS
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Glacial conditions may have inhibited
photosynthesis by stromatolites.
As a result, CO2 may have accumulated periodically
and triggered short episodes of global warming.
This produces the paradox of glaciers causing their
own destruction.
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RIFTING IN RODINIA
Around 570 million years ago, rifting began again,
and South America began to separate from North
America, forming the Iapetus Ocean (or protoAtlantic Ocean).
The rift ran along what is now the Blue Ridge
province. Basaltic lava flows formed the Catoctin
Formation.
As the Iapetus Ocean opened, sands and silts were
deposited in the shelf areas.
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PROTEROZOIC ROCKS SOUTH
OF THE CANADIAN SHIELD
Extensive outcrops of
Precambrian rocks are
present in the
Canadian Shield.
Precambrian rocks are also present in other areas,
including:
 Rocky Mountains
 Colorado Plateau (Grand Canyon)
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EVENTS RECORDED IN
PROTEROZOIC ROCKS
1.
2.
3.
4.
Collision of an Archean terrane with volcanic island
arc, 1.7 or 1.8 b.y.a. (Wyoming and western
Colorado)
Extensive magma intrusion in Mesoproterozoic,
1.5–1.4 b.y.a. (California to Labrador)
Widespread rifting
Rifts with thick sequences of shallow water
Neoproterozoic sedimentary rocks, 1.4–0.85 b.y.a.
Belt Supergroup (Glacier National Park, Montana,
Idaho, and British Columbia).
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PRECAMBRIAN ROCKS OF THE
GRAND CANYON
Vishnu Schist
metasediments and
gneisses, intruded
by Zoroaster
Granite about 1.4
b.y. to 1.3 b.y.a.
during the Mazatzal
orogeny.
Top of Vishnu Schist is
an unconformity.
FIGURE 9-15 Vishnu Schist, Grand Canyon
Supergroup, and other rocks in the Grand
Canyon of the Colorado River.
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PRECAMBRIAN ROCKS OF THE
GRAND CANYON
Grand Canyon
Supergroup
unconformably overlies
the Vishnu Schist while
unconformably
underling the
Paleozoic rocks.
The Grand Canyon
Supergroup consist of
Neoproterozoic
sandstones, siltstones,
and shales. Correlates
with Belt Supergroup.
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FIGURE 9-15 Vishnu Schist, Grand Canyon
Supergroup, and other rocks in the Grand
Canyon of the Colorado River.
LIFE AT THE BEGINNING OF
PROTEROZOIC WAS SIMILAR TO THAT
OF ARCHEAN
1.
2.
3.
4.
5.
Archaea in deep sea hydrothermal vents
Planktonic prokaryotes floated in seas and lakes
Anaerobic prokaryotes in oxygen-deficient
environments
Photosynthetic cyanobacteria (prokaryotes)
constructed stromatolites (algal filaments)
Eukaryotes (as indicated by molecular fossils)
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OTHER FORMS OF LIFE APPEARED
DURING PROTEROZOIC
1.
2.
3.
4.
More diverse eukaryotes including acritarchs
Metazoans or multicellular animals with soft
bodies
Metazoans with tiny calcium carbonate tubes or
shells
Metazoans that left burrows in the sediment
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MICROFOSSILS OF THE GUNFLINT CHERT

First definitive Precambrian fossils to be discovered
(in 1953) were in the 1.9 b.y. old Gunflint Chert,
NW of Lake Superior (Paleoproterozoic).
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MICROFOSSILS OF THE GUNFLINT CHERT
The fossils are well-preserved, abundant and diverse
and include:
 String-like filaments
 Spherical cells
 Filaments with cells separated by septae
(Gunflintia)
 Finely separate forms resembling living algae
(Animikiea)
 Star-like forms resembling living iron- and
magnesium-reducing bacteria (Eoastrion)
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MICROFOSSILS OF THE GUNFLINT CHERT
A = Eoastrion ( = dawn star),
probably iron- or magnesiumreducing bacteria
B = Eosphaera, an organism or
uncertain affinity, about 30
micrometers in diameter
C = Animikiea (probably algae)
D = Kakabekia, an organism or
uncertain affinity
FIGURE 9-20 (A) Eoastrion, (B)
Eosphaera, (C) Animikiea, and (D)
Kakabekia from the Gunflint Chert.
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MICROFOSSILS OF THE GUNFLINT CHERT
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Gunflint fossil organisms resemble photosynthetic
organisms.
The rock containing these organisms contains
organic compounds that are regarded as the
breakdown products of chlorophyll.
The Gunflint Chert organisms altered the
composition of the atmosphere by producing
oxygen.
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THE RISE OF EUKARYOTES
The appearance of eukaryotes is a major event during the history
of life.
Eukaryotes have the potential for sexual reproduction, which
increases variation through genetic recombination.
Genetic recombination provides greater possibilities for
evolutionary change.
Diversification of life probably did not occur until after the
advent of sexual reproduction, or until oxygen levels reached a
critical threshold.
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THE RISE OF EUKARYOTES
Eukaryotic cells can be
differentiated from
prokaryotic cells on the
basis of size.
Eukaryotes tend to be
much larger than
prokaryotes (larger than
60 microns, as compared
with less than 20
microns).
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Harold Levin
FIGURE 8-37 (A) Comparison of a
prokaryote cell (left) and a eukaryote cell.
THE RISE OF EUKARYOTES
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Eukaryotes appeared by Archean (as determined by
molecular fossils or biochemical remains).
Larger cells begin to appear in the fossil record by
2.7 b.y. to 2.2 b.y.
Eukaryotes began to diversity about 1.2 to 1.0 b.y.
ago.
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ACRITARCHS
1.
2.
3.
4.
5.
6.
Eukaryotes
Single-celled, spherical microfossils
Thick organic covering
May have been phytoplankton
First appeared 1.6 b.y. ago (at
Paleoproterozoic-Mesoproterozoic boundary)
Some resemble cysts or resting stages of
modern marine algae called dinoflagellates.
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ACRITARCHS
Reached maximum diversity and abundance
850 m.y. ago
8. Declined during Neoproterozoic glaciation
9. Few acritarchs remained by 675 m.y. ago
10. Extinction during Ordovician
11. Useful for correlating Proterozoic strata
7.
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THE FIRST METAZOANS
(MULTICELLULAR ANIMALS)
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Metazoans are multicellular animals with various
types of cells organized into tissues and organs.
Metazoans first appeared during Neoproterozoic,
about 630 m.y. ago (0.63 b.y.). Preserved as
impressions of soft-bodied organisms in
sandstones.
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EXAMPLES OF METAZOAN FOSSILS
IN PROTEROZOIC ROCKS
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Ediacara fauna: Imprints of soft-bodied organisms,
first found in Australia during the 1940s
Metazoan eggs and embryos in uppermost
Neoproterozoic Doushantuo Formation, south China
Trace fossils of burrowing metazoans in rocks
younger than the Varangian glaciation.
Tiny shell-bearing fossils (small shelly fauna)
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EDIACARA FAUNA
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Ediacara fauna is an important record of the first
evolutionary radiation of multicellular animals.
Some were probably ancestral to Paleozoic
invertebrates.
Oldest Ediacara-type fossils are from China.
Youngest Edicara-type fossils are Cambrian (510
m.y., Ireland).
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TYPES OF EDIACARA FOSSILS
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Discoidal
Frondlike
Elongate or ovate
FIGURE 9-28 Reconstruction of Kimberella.
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EDIACARA FAUNA
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
Because the Ediacara creatures are not really
similar to animals that are living today, this has led
to the suggestion that they be placed in a separate
taxonomic category or new phylum.
The name proposed for this new category is
Vendoza (named after the Vendian, or the latest
part of the Neoproterozoic in Russia).
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SMALL SHELLY FAUNA:
THE ORIGIN OF HARD PARTS
Small fossils with hard parts or shells
appeared during Neoproterozoic.
Cloudina, an organism with a small,
tubular shell of calcium carbonate
(CaCO3).
Resembles structures built by a tubedwelling annelid worm.
Earliest known organism with a
CaCO3 shell.
Found in Namibia, Africa.
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FIGURE 9-29 Cloudina, the
earliest known calcium
carbonate shell-bearing fossils.
SMALL SHELLY FAUNA:
THE ORIGIN OF HARD PARTS
Other latest Proterozoic and earliest Cambrian small fossils
with shells include:
 Possible primitive molluscs
 Sponge spicules,
 Tubular or cap-shaped shells, and
 Tiny tusk-shaped fossils called hyoliths
Some early shelly material is made of calcium phosphate.
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PRECAMBRIAN TRACE FOSSILS
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Trails, burrows, and other trace
fossils are found in Upper
Neoproterozoic rocks.
In rocks deposited after
Neoproterozoic Varangian glaciation.
Mostly simple, shallow burrows.
Trace fossils increase in diversity,
complexity, and number in younger
(Cambrian) rocks.
H. J. Hofman
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WHAT STIMULATED THE APPEARANCE
OF METAZOANS?
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
May be related to the accumulation of sufficient
oxygen in the atmosphere to support an oxygenbased metabolism.
Ancestral metazoans may have lived in "oxygen
oases" of marine plants.
Ediacaran life may have evolved gradually from
earlier forms that did not leave a fossil record.
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REVIEW OF
PROTEROZOIC
EVENTS
FIGURE 9-1 Pathway through the
Proterozoic, depicting major geologic
events.
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IMAGE CREDITS
• FIGURE 9-31 Correlation of major events in the biosphere, lithosphere, and
atmosphere.
• FIGURE 9-1 Pathway through the Proterozoic, depicting major geologic events.
Source: Harold Levin.
• FIGURE 9-10 The supercontinent Rodinia as it appeared about 1100 million years
ago. Source: Hoffman, 1991, Did the Breakout of Laurentia Turn Gondwanaland
Inside-Out?, The American Association for the Advancement of Science.
• FIGURE 9-11 Earth has seen several major episodes of widespread continental
glaciation (orange). Source: Harold Levin.
• FIGURE 9-15 Vishnu Schist, Grand Canyon Supergroup, and other rocks in the
Grand Canyon of the Colorado River.
• FIGURE 9-20 (A) Eoastrion, (B) Eosphaera, (C) Animikiea, and (D) Kakabekia
from the Gunflint Chert. Source: Barghoorn, E., 1971. "The Oldest Fossils,"
Scientific American 224:30-42.
• FIGURE 9-28 Reconstruction of Kimberella. Source: Harold Levin.
• FIGURE 9-29 Cloudina, the earliest known calcium carbonate shell-bearing
fossils. Source: Harold Levin.
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