Proterozoic Eon

THE PROTEROZOIC EON OF PRECAMBRIAN TIME

2.5 b.y. - 544 m.y. Eras:

Paleoproterozoic (2.5-1.6 b.y.)
Mesoproterozoic (1.6-1.0 b.y.) (Not necessary to memorize any of these)
Neoproterozoic (1.0 b.y.-544 m.y.)

Important Topics

Modern style orogenesis
Glaciations
Evolution of the atmosphere
Proterozoic evolution of North America
The formation of Rodinia
Origin of eukaryotes
Life evolution through the fossil record

MODERN STYLE OROGENY: Woopmay Orogen in the Slave Province

magmatic arc core
regional metamorphic rocks
fold and thrust belt: flysch followed by molasse sediments

Origin: collision of Woopmay Craton with volcanic arc

GLACIATIONS: First about 2.3 b.y.a.
Four between 850 & 600 m.y.a.

Varangian Glaciation: (last one) affected every continent except Antarctica, => climate at the end of the Proterozoic extremely cold. Evidences: _______________, ____________________, ________________, striations.

ATMOSPHERE: Out gassed Archean atmosphere had very little oxygen,
Cyanobacteria => Photosynthesis => released O2 (late Archean)
Atm. build up not possible until oxygen sinks were filled (iron precipitation & pyrite)
Sinks filled at about 1.9 b.y.a.
Evidences:

Banded iron formations (BIF's) in 2 b.y.a. rocks
Paleosoils without iron older than 1.9 b.y.a.
Continental red beds younger than 1.9 b.y.a.

Ocean's surface O2 abundance => oxidation of N2 to nitrates = a nutrient for the expansion of planktonic eukaryotes.

DANCE OF THE CONTINENTS & ASSEMBLY OF NORTH AMERICA
Recall: Continents grow by suturing

another __________________
a ______________________
a _________________ ________________
metamorphosed cont. shelf sediments

Continents are reduced in size by

_________________________ (too slow to be relevant)
rifting

The North American craton grew South & East by accretion of crustal blocks, reaching as far south as northern Mexico.
Together with Greenland they formed _______________________________.

1.2-1.0 b.y.a. Laurentia started to rift apart but aborted. What is the evidence?

basaltic flows & dikes +
continental sediments => Keweenawan formation

Grenville orogeny (ended 1.0 b.y.a.) along Laurentia's _____________________ margin.
Sutured it to north South America (Gondwana continents to the E & SW)

The Grenville suture is part of the extensive suturing that joined most of the land masses into the super continent Rodinia (1 b.y.a)

800 m.y.a. Rodinia breaks up by the formation of the _______________ Ocean. Evidence?
The Belt Supergroup (Canada & N. USA: contains ____________________ & mud cracks filled with salt crystals)

   => shallow marine environment
   => rapidly subsiding basin
   => frequent transgressions & regressions => rifting

Pan-African Orogeny: Migration of the rifted portions of Laurentia brought it into collision along opposite sides of the African craton.
New supercontinent? Between 700 & 500 m.y.a. numerous crustal segments added to the African craton.
Climatic consequence of the supercontinent? __________________________ Huge land mass prevented the continent from receiving the warming effects from the ocean.

PROTEROZOIC LIFE

Early Proterozoic: similar to Archean

______________________ dominate

First eukaryotes: Archean; First eukaryote fossils: Proterozoic

Gunflint Flora (Lake Superior): Paleoproterozoic, prokaryotes only (2 b.y.)
Stromatolites become widespread: Mesoproterozoic

Origin of the advanced eukaryote cell

Early eukaryotes very similar to prokaryotes & unicellular
Advanced eukaryotes needed to evolve cytoskeleton (engulfing ability)
One prokaryotic cell came to reside within the other (was engulfed)

Engulfed cell became the mitochondrion
Mitochondria helps host cell to ______________ ____________ ____ ________________ (respiration)
Mitochondrial DNA & RNA ______________________ from host cell

Similarly,

a cyanobacterium engulfed within another cell originated the chloroplasts

chloroplasts are the site of photosynthesis
chloroplasts & cyanobacteria have ___________________________
Chloroplast's DNA & RNA__________________________from host cell

ALGAE
First advanced eukaryotes were unicellular, but first advanced eukaryote fossils were multicellular, seaweed like algae.
Eukaryotes became more abundant after 2 b.y. (after sea ________________________________)
Acritachs: resting state of ____________________________? (plant-like protists)
ornamentation became more elaborate through the eon
many species extinct & replaced after Varangian glaciation.

EVOLUTION AND RADIATION OF METAZOAN FAUNA

First multicellular animals were ___________________ _____________________.
Known from trace fossils, soft body prints & few skeletal parts.
____________________________ fauna (Australia): cnidarians, annelids, arthropods and mollusks

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