the Proterozoic Eon alone,

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the Proterozoic Eon alone,

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Title: the Proterozoic Eon alone,

1
The Length of the Proterozoic

the Proterozoic Eon alone,
at 1.955 billion years long,
accounts for 42.5 of all geologic time
yet we review this long episode of Earth and life
history in a single section

2
The Phanerozoic

Yet the Phanerozoic,
consisting of
Paleozoic,
Mesozoic,
Cenozoic eras,
lasted a comparatively brief 545 million years
is the subject of the rest of the course

3
The Proterozoic EonTop Ten Significant Events

Plate tectonics occurred similar to modern rates
Accretion at continental boundaries
Assembly of Laurentia and two super continents
Widespread sandstone, carbonate, shale deposits
(continental shelf deposits)
Extensive continental glaciation
Mid-continent rift formed in North America
Widespread occurrence of stromatolites
Formation of banded iron and other mineral
resources (gold, copper, platinum, nickel)
Free oxygen in atmosphere
Evolution of eukaryotic cells

4
Style of Crustal Evolution

Archean crust-forming processes generated
granite-gneiss complexes
and greenstone belts
that were shaped into cratons
During the Proterozoic, these formed at a
considerably reduced rate and cooler temperatures

5
Contrasting Metamorphism

Many Archean rocks have been metamorphosed,
However, vast exposures of Proterozoic rocks
show little or no effects of metamorphism,
and in many areas they are separated
from Archean rocks by a profound unconformity

6
Evolution of Proterozoic Continents

Archean cratons assembled during collisions of
island arcs and minicontinents,
providing the center of todays continents.
Proterozoic crust accreted, at edges forming much
larger landmasses
Proterozoic accretion at craton margins
probably took place more rapidly than today
Earth possessed more radiogenic heat,
but the process continues even now

7
Proterozoic Greenstone Belts

They were not as common after the Archean,
near absence of ultramafic rocks
WHY would this happen?

8
Focus on Laurentia

Our focus here is on the geologic evolution of
Laurentia,
a large landmass that consisted of what is now
North America,
Greenland,
parts of northwestern Scotland,
and perhaps some of the Baltic shield of
Scandinavia

9
Early Proterozoic History of Laurentia

Laurentia originated 2.0 billion years ago
collisions called orogens
formed linear or arcuate deformation belts
in which many of the rocks have been
metamorphosed
and intruded by magma
thus forming plutons, especially batholiths

10
Proterozoic Evolution of Laurentia

Archean cratons were sutured
along deformation belts called orogens,
By 1.8 billion years ago,
much of what is now Greenland, central Canada,
and the north-central United States existed

Laurentia grew along its southern margin
by accretion

11
What is the evidence?Craton-Forming Processes

Recorded in rocks
In northwestern Canada
where the Slave and Rae cratons collided

12
Craton-Forming Processes

the Trans Hudson orogen
in Canada and the United States,
where the Superior, Hearne, and Wyoming cratons
were sutured
The southern margin of Laurentia
is the site of the Penokian orogen

13
Wilson Cycle

Rocks of the Wopmay orogen
in northwestern Canada are important
because they record the Wilson cycle
opening and closing of an ocean basin
A complete Wilson cycle,
named for the Canadian geologist J. Tuzo Wilson,
involves
fragmentation of a continent (rifting)
opening of an ocean basin
followed by closing of an ocean basin,
and finally reassembly of the continent

14
Wopmay Orogen

Some of the rocks in Wopmay orogen
are sandstone-carbonate-shale assemblages,
a suite of rocks typical of passive continental
margins
that first become widespread during the
Proterozoic

15
Early Proterozoic Rocks in Great Lakes Region
Evidence of continental shelf

Early Proterozoic sandstone-carbonate-shale
assemblages are widespread near the Great Lakes

16
Where? N. MichiganOutcrop of Sturgeon Quartzite

The sandstones have a variety of sedimentary
structures
such as
ripple marks
and cross-beds
Northern Michigan

17
Outcrop of Kona Dolomitewarm shallow marine

Some of the carbonate rocks, now mostly
dolostone,
such as the Kona Dolomite,
contain abundant bulbous structures known as
stromatolites
NorthernMichigan

18
Penokean Orogen

These rocks of northern Michigan
have been only moderately deformed
and are now part of the Penokean orogen

19
Southern Margin Accretion

Laurentia grew along its southern margin
by accretion of the Central Plains, Yavapai, and
Mazatzal orogens

Also notice that the Midcontinental Rift
had formed in the Great Lakes region by this time

20
BIF, Red Beds, Glaciers

This was also the time during which
most of Earths banded iron formations (BIF)
were deposited
The first continental red beds
sandstone and shale with oxidized iron
were deposited about 1.8 billion years ago
We will have more to say about BIF
and red beds in the section on The Evolving
Atmosphere
In addition, some Early Proterozoic rocks
provide excellent evidence for widespread
glaciation

21
Proterozoic Igneous Activity

These igneous rocks are exposed
in eastern Canada, extend across Greenland,
and are also found in the Baltic shield of
Scandinavia

22
Igneous ActivityWhy? How do we know?

However, the igneous rocks are deeply buried
by younger rocks in most areas
The origin of these
are the subject of debate
According to one hypothesis
large-scale upwelling of magma
beneath a Proterozoic supercontinent
produced the rocks

23
Middle Proterozoic Orogeny and Rifting

The only Middle Proterozoic event in Laurentia
was the Grenville orogeny
in the eastern part of the continent
1.3 to 1.0 billion years old
Grenville rocks are well exposed
in the present-day northern Appalachian Mountains
as well as in eastern Canada, Greenland, and
Scandinavia

24
Grenville Orogeny

A final episode of Proterozoic accretion
occurred during the Grenville orogeny

25
75 of North America

By this final stage, about 75
of present-day North America existed
The remaining 25
accreted along its margins,
particularly its eastern and western margins,
during the Phanerozoic Eon

26
Midcontinent Rift

Grenville deformation in Laurentia
was accompanied by the origin
of the Midcontinent rift,
a long narrow continental trough bounded by
faults,
extending from the Lake Superior basin southwest
into Kansas,
and a southeasterly branch extends through
Michigan into Ohio
It cuts through Archean and Early Proterozoic
rocks
and terminates in the east against rocks
of the Grenville orogen

27
Location of the Midcontinent Rift

Rocks filling the rift
are exposed around Lake Superior
but are deeply buried elsewhere

28
Midcontinental Rift

Most of the rift is buried beneath younger rocks
except in the Lake Superior region
with various igneous and sedimentary rocks
exposed
The Evidence
numerous overlapping basalt lava flows
forming a volcanic pile several kilometers thick

29
Portage Lake Volcanics

Michigan

30
Sedimentary Rocks

Middle to Late Proterozoic sedimentary rocks
are exceptionally well exposed
in the northern Rocky Mountains
of Montana and Alberta, Canada
Glacier National Park

31
Proterozoic Rocks, Glacier NP

Proterozoic sedimentary rocks
in Glacier National Park, Montana
The angular peaks, ridges and broad valleys
were carved by Pleistocene and Recent glaciers

32
Proterozoic Mudrock

Outcrop of red mudrock in Glacier National Park,
Montana

33
Proterozoic Limestone

Outcrop of limestone with stromatolites in
Glacier National Park, Montana

34
Grand Canyon Super-group

Proterozoic Sandstone of the Grand Canyon
Super-group in the Grand Canyon Arizona

35
Proterozoic Supercontinents

A supercontinent consists of all
Or much of the present-day continents,
so other than size it is the same as a continent
The supercontinent Pangaea,
existed MUCH LATER but few people are aware of
earlier supercontinents

36
Early Supercontinents

Rodinia
assembled between 1.3 and 1.0 billion years ago
and then began fragmenting (rifting apart) 750
million years ago (THE Proterozoic ends at 545my
ago)

37
Early Supercontinent

Possible configuration
of the Late Proterozoic supercontinent Rodinia
before it began fragmenting about 750 million
years ago

Rodinia's separate pieces reassembled
and formed another supercontinent
Pannotia
about 650 million years ago
Fragmentation was underway again,
about 550 million years ago,
giving rise to the continental configuration
that existed at the onset of the Phanerozoic Eon
the Cambrian

39
Recognizing Glaciation

How can we be sure that there were Proterozoic
glaciers?
the extensive geographic distribution
of other conglomerates and tillites
and their associated glacial features
is distinctive,
such as striated and polished bedrock

40
Proterozoic Glacial Evidence

Bagganjarga Tillite in Norway
Over bedrock

41
Geologists Convinced

The occurrence of tillites
in Michigan, Wyoming, and Quebec
indicates that North America may have had
an Early Proterozoic ice sheet centered southwest
of Hudson Bay

42
Early Proterozoic Glaciers

Deposits in North America
indicate that Laurentia
had an extensive ice sheet
centered southwest of Hudson Bay

43
Late Proterozoic Glaciers

The approximate distribution of Late Proterozoic
glaciers

Late Proterozoic glaciers
seem to have been present even
in near-equatorial areas!!
Geologists have recently named this phenomenon
SNOWBALL EARTH

45
The Evolving Atmosphere

Archean little or no free oxygen
the amount present
at the beginning of the Proterozoic was probably
no more than 1 of that present now
Stromatolitesnot common until
2.3 billion years ago,
that is, during the Early Proterozoic
There is evidence of increasing oxygen.

46
Early Proterozoic Banded Iron Formation

At this outcrop in Ishpeming, Michigan
the rocks are alternating layers of
red chert
and silver-colorediron minerals

47
Banded Iron Formations (BIF)

Banded iron formations (BIFs),
consist of alternating layers of
iron-rich minerals
and chert
about 92 of all BIFs
formed during the interval
from 2.5 to 2.0 billion years ago

48
BIFs and the Atmosphere

How are these rocks related to the atmosphere?
Their iron is in iron oxides, especially
hematite (Fe2O3)
and magnetite (Fe3O4)
Iron combines with oxygen in an oxidizing
atmosphere
to from rustlike oxides
that are not readily soluble in water
If oxygen is absent in the atmosphere, though,
iron easily dissolves
so that large quantities accumulate in the
world's oceans,
which it undoubtedly did during the Archean

49
Formation of BIFs

The Archean atmosphere was deficient in free
oxygen
so that little oxygen was dissolved in seawater
However, as photosynthesizing organisms
increased in abundance,
as indicated by stromatolites,
free oxygen,
released as a metabolic waste product into the
oceans,
caused the precipitation of iron oxides along
with silica
and thus created BIFs

50
Formation of BIFs

Depositional model for the origin of banded iron
formation

51
Source of Iron and Silica

A likely source of the iron and silica
was submarine volcanism,
similar to that now talking place
at or near spreading ridges
Huge quantities of dissolved minerals are
also discharged at submarine hydrothermal vents
In any case, the iron and silica
combined with oxygen
thus resulting in the precipitation
of huge amounts of banded iron formation
Precipitation continued until
the iron in seawater was largely used up

52
Continental Red Beds

Obviously continental red beds refers
to red rocks on the continents,
but more specifically it means red sandstone or
shale
colored by iron oxides,
especially hematite (Fe2O3)

Red mudrock in Glacier National Park, Montana
53
Red Beds

Red beds first appear
in the geologic records about 1.8 billion years
ago,
increase in abundance throughout the rest of the
Proterozoic,
and are quite common in rocks of Phanerozoic age
The onset of red bed deposition
coincides with the introduction of free oxygen
into the Proterozoic atmosphere
However, the atmosphere at that time
may have had only 1
or perhaps 2 of present levels

54
Red Beds

Is this percentage sufficient to account
for oxidized iron in sediment?
Probably not,
but no ozone (O3) layer existed in the upper
atmosphere
before free oxygen (O2) was present
As photosynthesizing organisms released
free oxygen into the atmosphere,
ultraviolet radiation converted some of it
to elemental oxygen (O) and ozone (O3),
both of which oxidize minerals more effectively
than O2

55
Red Beds

Once an ozone layer became established,
most ultraviolet radiation failed
to penetrate to the surface,
and O2 became the primary agent
for oxidizing minerals

56
Important Events in Life History

Archean fossils are not very common,
and all of those known are varieties
of bacteria and cyanobacteria (blue-green algae),
although they undoubtedly existed in profusion
Likewise, the Early Proterozoic fossil record
has mostly bacteria and cyanobacteria
Apparently little diversification
had taken place
all organisms were single-celled prokaryotes,
until about 2.1 billion years ago
when more complex eukaryotic cells evolved

57
Gunflint Microfossils

Even in well-known Early Proterozoic fossils
assemblages, only fossils of bacteria are
recognized

Photomicrograph of spheroidal and filamentous
microfossils from the Gunflint Chert of Ontario
Canada
58
Prokaryote and Eukaryotes

An organism made up of prokaryotic cells is
called a prokaryote
whereas those composed of eukaryotic cells are
eukaryotes
In fact, the distinction between prokaryotes and
eukaryotes
is the basis for the most profound distinction
between all living things

59
Lack of Organic Diversity

Actually, the lack of organic diversity
during this early time in life history
is not too surprising
because prokaryotic cells reproduce asexually
Most variation in
sexually reproducing populations comes from
the shuffling of genes,
and their alleles,
from generation to generation
Mutations introduce new variation into a
population,
but their effects are limited in prokaryotes

60
Genetic Variation in Bacteria

A beneficial mutation would spread rapidly
in sexually reproducing organism,
but have a limited impact in bacteria
because they do not share their genes with other
bacteria
Bacteria usually reproduce by binary fission
and give rise to two cells
having the same genetic makeup
Under some conditions,
they engage in conjugation during
which some genetic material is transferred

61
Sexual Reproduction Increased the Pace of
Evolution

Prior to the appearance of cells capable of
sexual reproduction,
evolution was a comparatively slow process,
thus accounting for the low organic diversity
This situation did not persist
Sexually reproducing cells probably
evolved by Early Proterozoic time,
and the tempo of evolution increased

62
Eukaryotic Cells Evolve

The appearance of eukaryotic cells
marks a milestone in evolution
comparable to the development
of complex metabolic mechanisms
such as photosynthesis during the Archean
Where did these cells come from?
How do they differ from their predecessors,
the prokaryotic cells?
All prokaryotes are single-celled,
but most eukaryotes are multicelled,
the notable exception being the protistans

63
Eukaryotes

Most eukaryotes reproduce sexually,
in marked contrast to prokaryotes,
and nearly all are aerobic,
that is, they depend on free oxygen
to carry out their metabolic processes
Accordingly, they could not have evolved
before at least some free oxygen was present in
the atmosphere

64
Prokaryotic Cell

Prokaryotic cells
do not have a cell nucleus
do not have organelles
are smaller and not nearly as complex as
eukaryotic cells

65
Eukaryotic Cell

Eukaryotic cells have
a cell nucleus containing
the genetic material
and organelles

such as mitochondria
and plastids,
as well as chloroplasts in plant cells

66
Eukaryotic Fossil Cells

The Negaunee Iron Formation in Michigan
which is 2.1 billion years old
has yielded fossils now generally accepted
as the oldest known eukaryotic cells
Even though the Bitter Springs Formation
of Australia is much younger --1 billion yrs old
it has some remarkable fossils of single-celled
eukaryotes
that show evidence of meiosis and mitosis,
processes carried out only by eukaryotic cells

67
Evidence for Eukaryotes

Prokaryotic cells are mostly rather simple
spherical or platelike structures
Eukaryotic cells
are larger
much more complex
have a well-defined, membrane-bounded cell
nucleus, which is lacking in prokaryotes
have several internal structures
called organelles such as plastids and
mitochondria
their organizational complexity
is much greater than it is for prokaryotes

68
Acritarchs

Other organisms that were
almost certainly eukaryotes are the acritarchs
that first appeared about 1.4 billion years ago
they were very common by Late Proterozoic time
and were probably cysts of planktonic (floating)
algae

69
Acritarchs

These common Late Proterozoic microfossils
are probably from eukaryotic organisms
Acritarchs are very likely the cysts of algae

70
Late Proterozoic Microfossil

Numerous microfossils of organisms
with vase-shaped skeletons
have been found
in Late Proterozoic rocks
in the Grand Canyon
These too have tentatively been identified as
cysts of some kind of algae

71
Endosymbiosis and the Origin of Eukaryotic Cells

Eukaryotic cells probably formed
from several prokaryotic cells
that entered into a symbiotic relationship
Symbiosis,
involving a prolonged association of two or more
dissimilar organisms,
is quite common today
In many cases both symbionts benefit from the
association
as occurs in lichens,
once thought to be plants
but actually symbiotic fungi and algae

72
Endosymbiosis

In a symbiotic relationship,
each symbiont must be capable
of metabolism and reproduction,
but in some cases one symbiont
cannot live independently
This may have been the case
with Proterozoic symbiotic prokaryotes
that became increasingly interdependent
until the unit could exist only as a whole
In this relationship
one symbiont lived within the other,
which is a special type of symbiosis
called endosymbiosis

73
Evidence for Endosymbiosis

Supporting evidence for endosymbiosis
comes from studies of living eukaryotic cells
containing internal structures called organelles,
such as mitochondria and plastics,
which contain their own genetic material
In addition, prokaryotic cells
synthesize proteins as a single system,
whereas eukaryotic cells
are a combination of protein-synthesizing systems

74
Organelles Capable of Protein Synthesis

That is, some of the organelles
within eukaryotic cells are capable of protein
synthesis
These organelles
with their own genetic material
and protein-synthesizing capabilities
are thought to have been free-living bacteria
that entered into a symbiotic relationship,
eventually giving rise to eukaryotic cells

75
Multicelled Organisms

Obviously multicelled organisms
are made up of many cells,
perhaps billions,
as opposed to a single cell as in prokaryotes
In addition, multicelled organisms
have cells specialized to perform specific
functions
such as respiration,
food gathering,
and reproduction

76
Dawn of Multicelled Organisms

We know from the fossil record
that multicelled organisms were present during
the Proterozoic,
but we do not know exactly when they appeared
What seem to be some kind of multicelled algae
appear
in the 2.1-billion-year-old fossils
from the Negaunee Iron Formation in Michigan
as carbonaceous filaments
from 1.8 billion-year-old rocks in China
as somewhat younger carbonaceous impressions
of filaments and spherical forms

77
Multicelled Algae?

Carbonaceous impressions
in Proterozoic rocks, Montana
These may be impressions of multicelled algae
Skip next slide

78
The Multicelled Advantage?

Is there any particular advantage to being
multicelled?
For something on the order of 1.5 billion years
all organisms were single-celled
and life seems to have thrived
In fact, single-celled organisms
are quite good at what they do
but what they do is very limited

79
The Multicelled Advantage?

For example, single celled organisms
can not grow very large, because as size
increases proportionately less of a cell is
exposed to the external environment in relation
to its volume
and the proportion of surface area decreases
Transferring materials from the exterior
to the interior becomes less efficient

80
The Multicelled Advantage?

Also, multicelled organisms live longer,
since cells can be replaced and more offspring
can be produced
Cells have increased functional efficiency
when they are specialized into organs with
specific capabilities

81
Late Proterozoic Animals

Biologists set forth criteria such as
method of reproduction
and type of metabolism
to allow us to easily distinguish
between animals and plants
Or so it would seem,
but some present-day organisms
blur this distinction and the same is true
for some Proterozoic fossils
Nevertheless, the first
relatively controversy-free fossils of animals
come from the Ediacaran fauna of Australia
and similar faunas of similar age elsewhere

82
The Ediacaran Fauna

In 1947, an Australian geologist, R.C. Sprigg,
in the Pound Quartzite in the Ediacara Hills of
South Australia
Additional discoveries by others turned up what
appeared to be
discovered impressions of soft-bodied animals
impressions of algae and several animals
many bearing no resemblance to any existing now
Before these discoveries, geologists
were perplexed by the apparent absence
of fossil-bearing rocks predating the Phanerozoic

83
Ediacaran Fauna

The Ediacaran fauna of Australia
Tribrachidium heraldicum, a possible primitive
echinoderm

Spriggina floundersi, a possible ancestor of
trilobites
84
Ediacaran Fauna

Pavancorina minchami

Restoration of the Ediacaran Environment

85
Ediacaran Fauna

Geologists had assumed that
the fossils so common in Cambrian rocks
must have had a long previous history
but had little evidence to support this
conclusion
The discovery of Ediacaran fossils and subsequent
discoveries
have not answered all questions about
pre-Phanerozoic animals,
but they have certainly increased our knowledge
about this chapter in the history of life

86
Represented Phyla

Three present-day phyla may be represented
in the Ediacaran fauna
jellyfish and sea pens (phylum Cnidaria),
segmented worms (phylum Annelida),
and primitive members of the phylum Arthropoda
(the phylum with insects, spiders crabs, and
others)
One Ediacaran fossil, Spriggina,
has been cited as a possible ancestor of
trilobites
Another might be a primitive member
of the phylum Echinodermata

87
Distinct Evolutionary Group

However, some scientists think
these Ediacaran animals represent
an early evolutionary group quite distinct from
the ancestry of todays invertebrate animals
Ediacara-type faunas are known
from all continents except Antarctica,
--were widespread between 545 and 670 million
years ago
but their fossils are rare
Their scarcity should not be surprising, though,
because all lacked durable skeletons

88
Other Proterozoic Animal Fossils

Although scarce, a few animal fossils
older than those of the Ediacaran fauna are known
A jellyfish-like impression is present
in rocks 2000 m below the Ediacara Hills Pound
Quartzite,
Burrows, in many areas,
presumably made by worms,
occur in rocks at least 700 million years old
Wormlike and algae fossils come
from 700 to 900 million-year-old rocks in China
but the identity and age of these "fossils" has
been questioned

89
Wormlike Fossils from China

Wormlike fossils from Late Proterozoic rocks in
China

90
Soft Bodies

All known Proterozoic animals were soft-bodied,
but there is some evidence that the earliest
stages in the origin of skeletons was underway
Even some Ediacaran animals
may have had a chitinous carapace
and others appear to have had areas of calcium
carbonate
The odd creature known as Kimberella
from the latest Proterozoic of Russia
had a tough outer covering similar to
that of some present-day marine invertebrates

91
Latest Proterozoic Kimberella

Kimberella, an animal from latest Proterozoic
rocks in Russia

Exactly what Kimberella was remains uncertain
Some think it was a sluglike creature
whereas others think it was more like a mollusk

92
Durable Skeletons

Latest Proterozoic fossils
of minute scraps of shell-like material
and small tooth like denticles and spicules,
presumably from sponges
indicate that several animals with skeletons
or at least partial skeletons existed
However, more durable skeletons of
silica,
calcium carbonate,
and chitin (a complex organic substance)
did not appear in abundance until the beginning
of the Phanerozoic Eon 545 million years ago

93
Proterozoic Mineral Resources

Most of the world's iron ore comes from
Proterozoic banded iron formations
Canada and the United States have large deposits
of these rocks
in the Lake Superior region
and in eastern Canada
Thus, both countries rank among
the ten leading nations in iron ore production

94
Iron Mine

The Empire Mine at Palmer, Michigan
where iron ore from the Early Proterozoic
Negaunee Iron Formation is mined

95
Nickel

In the Sudbury mining district in Ontario,
Canada,
nickel and platinum are extracted from
Proterozoic rocks
Nickel is essential for the production of nickel
alloys such as
stainless steel
and Monel metal (nickel plus copper),
which are valued for their strength and
resistance to corrosion and heat
The United States must import
more than 50 of all nickel used
mostly from the Sudbury mining district

96
Sudbury Basin

Besides its economic importance, the Sudbury
Basin,
an elliptical area measuring more than 59 by 27
km,
is interesting from the geological perspective
One hypothesis for the concentration of ores
is that they were mobilized from metal-rich rocks
beneath the basin
following a high-velocity meteorite impact

97
Platinum and Chromium

Some platinum
for jewelry, surgical instruments,
and chemical and electrical equipment
is exported to the United States from Canada,
but the major exporter is South Africa
The Bushveld Complex of South Africa
is a layered igneous complex containing both
platinum
and chromite
the only ore of chromium,
United States imports much of the chromium
from South Africa
It is used mostly in stainless steel

98
Oil and Gas

Economically recoverable oil and gas
have been discovered in Proterozoic rocks in
China and Siberia,
arousing some interest in the Midcontinent rift
as a potential source of hydrocarbons
So far, land has been leased for exploration,
and numerous geophysical studies have been done
However, even though some rocks
within the rift are know to contain petroleum,
no producing oil or gas wells are operating

99
Proterozoic Pegmatites