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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 . The Length of the Proterozoic. the Proterozoic Eon alone, at 1.955 billion years long,

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proterozoic rocks glacier np
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
the length of the proterozoic
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
the phanerozoic
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
disparity in time
Disparity in Time
  • Perhaps this disparity
    • between the coverage of the Proterozoic and the Phanerozoic
    • seems disproportionate,
  • but we know far more
    • about Phanerozoic events
    • than we do for either of the Precambrian eons
archean proterozoic boundary
Archean-Proterozoic Boundary
  • Geologist have rather arbitrarily placed
    • the Archean-Proterozoic boundary
    • at 2.5 billion years ago
    • because it marks the approximate time
    • of changes in the style of crustal evolution
  • However, we must emphasize "approximate,"
    • because Archean-type crustal evolution
    • was largely completed in South Africa
    • nearly 3.0 billion years ago,
    • whereas in North America the change took place
    • from 2.95 to 2.45 billion years ago
style of crustal evolution
Style of Crustal Evolution
  • Archean crust-forming processes generated
    • granite-gneiss complexes
    • and greenstone belts
    • that were shaped into cratons
  • Although these same rock associations
    • continued to form during the Proterozoic,
    • they did so at a considerably reduced rate
contrasting metamorphism
Contrasting Metamorphism
  • In addition, Archean and Proterozoic rocks
    • contrast in metamorphism
  • Many Archean rocks have been metamorphosed,
    • although their degree of metamorphism
    • varies and some are completely unaltered
  • 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
other differences
Other Differences
    • In addition to changes in the style of crustal evolution,
  • the Proterozoic is characterized
    • by widespread rock assemblages
      • that are rare or absent in the Archean,
    • by a plate tectonic style essentially the same as that of the present
    • by important evolution of the atmosphere and biosphere
    • by the origin of some important mineral resources
proterozoic evolution of oxygen dependent organisms
Proterozoic Evolution of Oxygen-Dependent Organisms
  • It was during the Proterozoic
    • that oxygen-dependent organisms
    • made their appearance
  • and the first cells evolved
    • that make up most organisms today
evolution of proterozoic continents
Evolution of Proterozoic Continents
  • Archean cratons assembled during collisions
    • of island arcs and minicontinents,
    • providing the nuclei around which
    • Proterozoic crust accreted,
    • thereby forming much larger landmasses
  • Proterozoic accretion at craton margins
    • probably took place more rapidly than today
    • because Earth possessed more radiogenic heat,
    • but the process continues even now
proterozoic greenstone belts
Proterozoic Greenstone Belts
  • Most greenstone belts formed
    • during the Archean
    • between 2.7 and 2.5 billion years ago
  • They also continued to form
    • during the Proterozoic and at least one is known
    • from Cambrian-aged rocks in Australia
  • They were not as common after the Archean,
    • and differed in one important detail
      • the near absence of ultramafic rocks
      • which no doubt resulted from
      • Earth's decreasing amount of radiogenic heat
focus on laurentia
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
early proterozoic history of laurentia
Early Proterozoic History of Laurentia
  • Laurentia originated and underwent important growth
    • between 2.0 and 1.8 billion years ago
  • During this time, collisions
    • among various plates formed several orogens,
    • which are linear or arcuate deformation belts
    • in which many of the rocks have been
      • metamorphosed
      • and intruded by magma
      • thus forming plutons, especially batholiths
proterozoic evolution of laurentia
Proterozoic Evolution of Laurentia
  • Archean cratons were sutured
    • along deformation belts called orogens,
    • thereby forming a larger landmass
  • 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
craton forming processes
Craton-Forming Processes
  • Examples of these craton-forming processes
    • are recorded in rocks
    • in the Thelon orogen in northwestern Canada
      • where the Slave and Rae cratons collided,
craton forming processes1
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
wilson cycle
Wilson Cycle
  • Rocks of the Wopmay orogen
    • in northwestern Canada are important
    • because they record the opening and closing
    • of an ocean basin
    • or what is called a Wilson cycle
  • A complete Wilson cycle,
      • named for the Canadian geologist J. Tuzo Wilson,
    • involves
      • fragmentation of a continent,
      • opening followed by closing
      • of an ocean basin,
      • and finally reassembly of the continent
wopmay orogen
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
early proterozoic rocks in great lakes region
Early Proterozoic Rocks in Great Lakes Region
  • Early Proterozoic sandstone-carbonate-shale assemblages are widespread near the Great Lakes
outcrop of sturgeon quartzite
Outcrop of Sturgeon Quartzite
  • The sandstones have a variety of sedimentary structures
    • such as
    • ripple marks
    • and cross-beds
    • Northern Michigan
outcrop of kona dolomite
Outcrop of Kona Dolomite
  • Some of the carbonate rocks, now mostly dolostone,
    • such as the Kona Dolomite,
    • contain abundant bulbous structures known as stromatolites
    • NorthernMichigan
penkean orogen
Penkean Orogen
  • These rocks of northern Michigan
    • have been only moderately deformed
    • and are now part of the Penokean orogen
accretion along laurentia s southern margin
Accretion along Laurentia’s Southern Margin
  • Following the initial episode
    • of amalgamation of Archean cratons
      • 2.0 to 1.8 billion years ago
    • accretion took place along Laurentia's southern margin
  • From 1.8 to 1.6 billion years ago,
    • continental accretion continued
      • in what is now the southwestern and central United States
    • as successively younger belts were sutured to Laurentia,
    • forming the Yavapai and Mazatzal-Pecos orogens
southern margin accretion
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
bif red beds glaciers
BIF, Red Beds, Glaciers
  • This was also the time during which
    • most of Earth’s 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
    • and associated features provide excellent evidence
    • for widespread glaciation
early and middle proterozoic igneous activity
Early and Middle Proterozoic Igneous Activity
  • During the interval
    • from 1.8 to 1.1 billion years ago,
    • extensive igneous activity took place
    • that seems to be unrelated to orogenic activity
  • Although quite widespread,
    • this activity did not add to Laurentia’s size
    • because magma was either intruded into
    • or erupted onto already existing continental crust
igneous activity
Igneous Activity
  • These igneous rocks are exposed
    • in eastern Canada, extend across Greenland,
    • and are also found in the Baltic shield of Scandinavia
igneous activity1
Igneous Activity
  • However, the igneous rocks are deeply buried
    • by younger rocks in most areas
  • The origin of these
    • granitic and anorthosite plutons,
      • Anorthosite is a plutonic rock composed
      • almost entirely of plagioclase feldspars
    • calderas and their fill,
    • and vast sheets of rhyolite and ash flows
    • are the subject of debate
  • According to one hypothesis
    • large-scale upwelling of magma
    • beneath a Proterozoic supercontinent
    • produced the rocks
middle proterozoic orogeny and rifting
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
grenville orogeny
Grenville Orogeny
  • A final episode of Proterozoic accretion
    • occurred during the Grenville orogeny
grenville orogeny1
Grenville Orogeny
  • Many geologists think the Grenville orogen
    • resulted from closure of an ocean basin,
      • the final stage in a Wilson cycle
  • Others disagree and think
    • intracontinental deformation or major shearing
    • was responsible for deformation
  • Whatever the cause of the Grenville orogeny,
    • it was the final stage
    • in the Proterozoic continental accretion of Laurentia
75 of north america
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
midcontinent rift
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
location of the midcontinent rift
Location of the Midcontinent Rift
  • Rocks filling the rift
    • are exposed around Lake Superior
    • but are deeply buried elsewhere
midcontinental rift
Midcontinental Rift
  • Most of the rift is buried beneath younger rocks
    • except in the Lake Superior region
    • where various igneous and sedimentary rocks
    • are well exposed
  • The central part of the rift contains
    • numerous overlapping basalt lava flows
    • forming a volcanic pile several kilometers thick
  • In fact, the volume of volcanic rocks,
    • between 300,000 and 1,000,000 km3,
    • is comparable in volume although not areal extent
    • to the great outpourings of lava during the Cenozoic
midcontinental rift1
Midcontinental Rift
  • Along the rift's margins
    • coarse-grained sediments were deposited
    • in large alluvial fans
    • that grade into sandstone and shale
    • with increasing distance
    • from the sediment source
  • In the vertical section
    • Freda Sandstone overlies
    • Cooper Harbor conglomerate,
    • which overlies Portage Lake Volcanics
middle and late proterozoic sedimentation
Middle and Late Proterozoic Sedimentation
  • Remember the Grenville orogeny
    • took place 1.2 billion – 900 million years ago,
    • the final episode of continental accretion
    • in Laurentia until the Ordovician Period
  • Nevertheless, important geologic events
    • were taking place,
    • such as sediment deposition in what is now
    • the eastern United States and Canada,
    • in the Death Valley region of California and Nevada,
    • and in three huge basins in the west
sedimentary basins in the west
Sedimentary Basins in the West
  • Map showing the locations of sedimentary Basins
    • in the western United States and Canada
      • Belt Basin
      • Uinta Basin
      • Apache Basin
sedimentary rocks
Sedimentary Rocks
  • Middle to Late Proterozoic sedimentary rocks
    • are exceptionally well exposed
    • in the northern Rocky Mountains
    • of Montana and Alberta, Canada
  • Indeed, their colors, deformation features,
    • and erosion by Pleistocene and recent glaciers
    • have yielded some fantastic scenery
  • Like the rocks in the Great Lakes region
    • and the Grand Canyon,
    • they are mostly sandstones, shales,
    • and stromatolite-bearing carbonates
proterozoic mudrock
Proterozoic Mudrock
  • Outcrop of red mudrock in Glacier National Park, Montana
proterozoic limestone
Proterozoic Limestone
  • Outcrop of limestone with stromatolites in Glacier National Park, Montana
proterozoic sandstone
Proterozoic Sandstone
  • Proterozoic rocks
    • of the Grand Canyon Super-group lie
    • unconformably upon Archean rocks
    • and in turn are overlain unconformably
    • by Phanerozoic-age rocks
  • The rocks, consisting mostly
    • of sandstone, shale, and dolostone,
    • were deposited in shallow-water marine
    • and fluvial environments
  • The presence of stromatolites and carbonaceous
    • impression of algae in some of these rocks
    • indicate probable marine deposition
grand canyon super group
Grand Canyon Super-group
  • Proterozoic Sandstone of the Grand Canyon Super-group in the Grand Canyon Arizona
style of plate tectonics
Style of Plate Tectonics
  • The present style of plate tectonics
    • involving opening and then closing ocean basins
    • had almost certainly been established by the Early Proterozoic
  • In fact, the oldest known complete ophiolite
    • providing evidence for an ancient convergent plate boundary
    • is the Jormua mafic-ultramafic complex in Finland
  • It is about 1.96 billion years old,
    • but nevertheless compares closely in detail
    • with younger well-documented ophiolites
jormua complex finland
Jormua Complex, Finland
  • Reconstruction
    • of the highly deformed
    • Jormua mafic-ultramafic complex
    • in Finland
  • This sequence of rock
    • is the oldest known complete ophiolite
    • at 1.96 billion years old
jormua complex finland1
Jormua Complex, Finland
  • Metamorphosed basaltic pillow lava

12 cm

jormua complex finland2
Jormua Complex, Finland
  • Metamorphosed gabbro between mafic dikes

65 cm

proterozoic supercontinents
Proterozoic Supercontinents
  • You already know that a continent
    • is one of Earth's landmasses
    • consisting of granitic crust
    • with most of its surface above sea level
  • A supercontinent consists of all
    • or at least much of the present-day continents,
    • so other than size it is the same as a continent
  • The supercontinent Pangaea,
    • which existed at the end of the Paleozoic Era,
    • is familiar,
    • but few people are aware of earlier supercontinents
early supercontinents
Early Supercontinents
  • Supercontinents may have existed
    • as early as the Late Archean,
    • but if so we have little evidence of them
  • The first that geologists recognize
    • with some certainty, known as Rodinia
    • assembled between 1.3 and 1.0 billion years ago
    • and then began fragmenting 750 million years ago
early supercontinent
Early Supercontinent
  • Possible configuration
    • of the Late Proterozoic supercontinent Rodinia
    • before it began fragmenting about 750 million years ago
pannotia
Pannotia
  • Rodinia's separate pieces reassembled
    • and formed another supercontinent
    • this one known as Pannotia
    • about 650 million years ago
    • judging by the Pan-African orogeny
      • the large-scale deformation that took place
      • in what are now the Southern Hemisphere continents
  • Fragmentation was underway again,
    • by the latest Proterozoic, about 550 million years ago,
    • giving rise to the continental configuration
    • that existed at the onset of the Phanerozoic Eon
ancient glaciers
Ancient Glaciers
  • Very few times of widespread glacial activity
    • have occurred during Earth history
  • The most recent one during the Pleistocene
    • 1.6 million to 10,000 years ago
    • is certainly the best known,
    • but we also have evidence for Pennsylvanian glaciers
    • and two major episodes of Proterozoic glaciation
recognizing glaciation
Recognizing Glaciation
  • How can we be sure that there were Proterozoic glaciers?
    • After all, their most common deposit
    • called tillite is simply a type of conglomerate
    • that may look much like conglomerate
    • that originated by other processes
  • Tillite or tillite-like deposits are known
    • from at least 300 Precambrian localities,
    • and some of these are undoubtedly not glacial deposits
glacial evidence
Glacial Evidence
  • But the extensive geographic distribution
    • of other conglomerates
    • and their associated glacial features
    • is distinctive,
    • such as striated and polished bedrock
proterozoic glacial evidence
Proterozoic Glacial Evidence
  • Bagganjarga tillite in Norway
    • overlies striated bedrock surface
    • on sandstone of the Veidnesbotn Formation
geologists convinced
Geologists Convinced
  • Geologists are now convinced
      • based on this kind of evidence
    • that widespread glaciation
    • took place during the Early Proterozoic
  • The occurrence of tillites of about the same age
    • in Michigan, Wyoming, and Quebec
    • indicates that North America may have had
    • an Early Proterozoic ice sheet centered southwest of Hudson Bay
early proterozoic glaciers
Early Proterozoic Glaciers
  • Deposits in North America
    • indicate that Laurentia
    • had an extensive ice sheet
    • centered southwest of Hudson Bay
one or more glaciations
One or More Glaciations?
  • Tillites of about this age are also found
    • in Australia and South Africa,
    • but dating is not precise enough to determine
    • if there was a single widespread glacial episode
    • or a number of glacial events at different times in different areas
  • One tillite in the Bruce Formation in Ontario, Canada
    • may date from 2.7 billion years ago,
    • thus making it Late Archean
glaciers of the late proterozoic
Glaciers of the Late Proterozoic
  • Tillites and other glacial features
    • dating from between 900 and 600 million years ago
    • are found on all continents except Antarctica
  • Glaciation was not continuous during this entire time
    • but was episodic with four major glacial episodes so far recognized
late proterozoic glaciers
Late Proterozoic Glaciers
  • The approximate distribution of Late Proterozoic glaciers
most extensive glaciation in earth history
Most Extensive Glaciation in Earth History
  • The map shows only approximate distribution
    • of Late Proterozoic glaciers
    • The actual extent of glaciers is unknown
  • Not all the glaciers were present at the same time
  • Despite these uncertainties,
    • this Late Proterozoic glaciation
    • was the most extensive in Earth history
  • In fact, Late Proterozoic glaciers
    • seem to have been present even
    • in near-equatorial areas
the evolving atmosphere
The Evolving Atmosphere
  • Geologists agree that the Archean atmosphere
    • contained little or no free oxygen so the atmosphere
    • was not strongly oxidizing as it is now
  • Even though processes were underway
    • that added free oxygen to the atmosphere,
    • the amount present
    • at the beginning of the Proterozoic
    • was probably no more than 1% of that present now
  • In fact, it might not have exceeded
    • 10% of present levels even
    • at the end of the Proterozoic
cyanobacteria and stromatolites
Cyanobacteria and Stromatolites
  • Remember from our previous discussions
    • that cyanobacteria,
      • also known as blue-green algae,
    • were present during the Archean,
    • but stromatolites
      • the structures they formed,
    • did not become common until about 2.3 billion years ago,
      • that is, during the Early Proterozoic
  • These photosynthesizing organisms
    • and to a lesser degree photochemical dissociation
  • added free oxygen to the evolving atmosphere
oxygen versus carbon dioxide
Oxygen Versus Carbon Dioxide
  • Earth's early atmosphere
    • had abundant carbon dioxide
  • More oxygen became available
    • whereas the amount of carbon dioxide decreased
  • Only a small amount of CO2
    • still exists in the atmosphere today
  • It is one of the greenhouse gases
    • partly responsible for global warming
  • What evidence indicates
    • that the atmosphere became oxidizing?
  • Where is all that additional the carbon dioxide now?
evidence from rocks
Evidence from Rocks
  • Much carbon dioxide is now tied up
    • in various minerals and rocks
      • especially the carbonate rocks
        • limestone and dolostone,
    • and in the biosphere
  • For evidence that the Proterozoic atmosphere was evolving
    • from a chemically reducing one
    • to an oxidizing one
  • we must discuss types
    • of Proterozoic sedimentary rocks, in particular
    • banded iron formations
    • and red beds
banded iron formations bif
Banded Iron Formations (BIF)
  • Banded iron formations (BIFs),
    • consist of alternating layers of
      • iron-rich minerals
      • and chert
    • Some are found in Archean rocks,
    • but about 92% of all BIFs
      • formed during the interval
      • from 2.5 to 2.0 billion years ago
early proterozoic banded iron formation
Early Proterozoic Banded Iron Formation
  • At this outcrop in Ishpeming, Michigan
  • the rocks are alternating layers of
  • red chert
  • and silver-colorediron minerals
typical bif
Typical BIF
  • A more typical outcrop of BIF near Nagaunee, Michigan
bifs and the atmosphere
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
formation of bifs
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
formation of bifs1
Formation of BIFs
  • One model accounting for the details
    • of BIF precipitation involves
    • a Precambrian ocean with an upper oxygenated layer
    • overlying a large volume of oxygen-deficient water
    • that contained reduced iron and silica
  • Upwelling,
    • that is transfer of water from depth to the surface,
    • brought iron- and silica-rich waters
    • onto the shallow continental shelves
    • and resulting in widespread precipitation of BIFs
formation of bifs2
Formation of BIFs
  • Depositional model for the origin of banded iron formation
source of iron and silica
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
continental red beds
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

red beds
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
red beds1
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
red beds2
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
important events in life history
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
gunflint microfossils
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

prokaryote and eukaryotes
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
lack of organic diversity
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
genetic variation in bacteria
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
sexual reproduction increased the pace of evolution
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
eukaryotic cells evolve
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
eukaryotes
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
prokaryotic cell
Prokaryotic Cell
  • Prokaryotic cells
    • do not have a cell nucleus
    • do not have organelles
    • are smaller and not nearly as complex as eukaryotic cells
eukaryotic cell
Eukaryotic Cell
  • such as mitochondria
  • and plastids,
  • as well as chloroplasts in plant cells
  • Eukaryotic cells have
    • a cell nucleus containing
    • the genetic material
    • and organelles
eukaryotic fossil cells
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
evidence for eukaryotes
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
acritarchs
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
acritarchs1
Acritarchs
  • These common Late Proterozoic microfossils
    • are probably from eukaryotic organisms
  • Acritarchs are very likely the cysts of algae
late proterozoic microfossil
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
endosymbiosis and the origin of eukaryotic cells
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
endosymbiosis
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
evidence for endosymbiosis
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
organelles capable of protein synthesis
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
multicelled organisms
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
dawn of multicelled organisms
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
multicelled algae
Multicelled Algae?
  • Carbonaceous impressions
    • in Proterozoic rocks, Montana
  • These may be impressions of multicelled algae
    • Skip next slide
the multicelled advantage
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
the multicelled advantage1
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
the multicelled advantage2
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
late proterozoic animals
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
the ediacaran fauna
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
ediacaran fauna
Ediacaran Fauna
  • The Ediacaran fauna of Australia

Tribrachidium heraldicum, a possible primitive echinoderm

Spriggina floundersi, a possible ancestor of trilobites

ediacaran fauna1
Ediacaran Fauna

Pavancorina minchami

  • Restoration of the Ediacaran Environment
ediacaran fauna2
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
represented phyla
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
distinct evolutionary group
Distinct Evolutionary Group
  • However, some scientists think
    • these Ediacaran animals represent
    • an early evolutionary group quite distinct from
    • the ancestry of today’s 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
other proterozoic animal fossils
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
wormlike fossils from china
Wormlike Fossils from China
  • Wormlike fossils from Late Proterozoic rocks in China
soft bodies
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
latest proterozoic kimberella
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
durable skeletons
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
proterozoic mineral resources
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
iron mine
Iron Mine
  • The Empire Mine at Palmer, Michigan
    • where iron ore from the Early Proterozoic Negaunee Iron Formation is mined
nickel
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
sudbury basin
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
platinum and chromium
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
oil and gas
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
proterozoic pegmatites
Proterozoic Pegmatites
  • A number of Proterozoic pegmatites
    • are important economically
  • The Dunton pegmatite in Maine,
    • whose age is generally considered
    • to be Late Proterozoic,
    • has yielded magnificent gem-quality specimens
    • of tourmaline and other minerals
  • Other pegmatites are mined for gemstones as well as for
    • tin, industrial minerals, such as feldspars, micas, and quartz
    • and minerals containing such elements
    • as cesium, rubidium, lithium, and beryllium
proterozoic pegmatites1
Proterozoic Pegmatites
  • Geologists have identified more than 20,000 pegmatites
    • in the country rocks adjacent
    • to the Harney Peak Granite
    • in the Black Hills of South Dakota
  • These pegmatites formed ~ 1.7 billion years ago
    • when the granite was emplaced as a complex of dikes and sills
  • A few have been mined for gemstones, tin, lithium, micas,
    • and some of the world's largest known
    • mineral crystals were discovered in these pegmatites
summary
Summary
  • The crust-forming processes
    • that yielded Archean granite-gneiss complexes
    • and greenstone belts
    • continued into the Proterozoic
    • but at a considerably reduced rate
  • Archean and Proterozoic greenstone belts
    • differed in detail
  • Early Proterozoic collisions
    • between Archean cratons formed larger cratons
    • that served as nuclei
    • around which Proterozoic crust accreted
summary1
Summary
  • One such landmass was Laurentia
    • consisting mostly of North America and Greenland
  • Important events
    • in the evolution of Laurentia were
      • Early Proterozoic amalgamation of cratons
      • followed by Middle Proterozoic igneous activity,
      • the Grenville orogeny, and the Midcontinent rift
  • Ophiolite sequences
    • marking convergent plate boundaries
    • are first well documented from the Early Proterozoic,
    • indicating that a plate tectonic style similar
    • to that operating now had been established
summary2
Summary
  • Sandstone-carbonate-shale assemblages
    • deposited on passive continental margins
    • are known from the Archean
    • but they are very common by Proterozoic time
  • The supercontinent Rodinia
    • assembled between 1.3 and 1.0 billion years ago,
    • fragmented,
    • and then reassembled to form Pannotia about 650 million years ago
  • Glaciers were widespread
    • during both the Early and Late Proterozoic
summary3
Summary
  • Photosynthesis continued
    • to release free oxygen into the atmosphere
    • which became increasingly oxygen rich through the Proterozoic
  • Fully 92% of Earth's iron ore deposits
    • in banded iron formations were deposited
    • between 2.5 and 2.0 billion years ago
  • Widespread continental red beds
    • dating from 1.8 billion years ago indicate
    • that Earth's atmosphere had enough free oxygen
    • for oxidation of iron compounds
summary4
Summary
  • Most of the known Proterozoic organisms
    • are single-celled prokaryotes (bacteria)
  • When eukaryotic cells first appeared is uncertain,
    • but they may have been present by 2.1 billion years ago
  • Endosymbiosis is a widely accepted theory for their origin
  • The oldest known multicelled organisms
    • are probably algae,
    • some of which may date back to the Early Proterozoic
summary5
Summary
  • Well-documented multicelled animals
    • are found in several Late Proterozoic localities
  • Animals were widespread at this time,
    • but because all lacked durable skeletons
    • their fossils are not common
  • Most of the world's iron ore produced
    • is from Proterozoic banded iron formations
  • Other important resources
    • include nickel and platinum