Proterozoic 1 Large cratons 2 Global glaciations 3 Orogeny mm 4 5 Biotic evolution multicellular organisms animals Intensive deposition in shallow seas 1 Fossil record is the basis for the division of Proterozoic eon in three basic a Paleoproterozoic 2 5 1 6 Ga b Mesoproterozoic 1 6 1 Ga c Neoproterozoic 1 0 54 Ga Introduction eras Orogeny building 2 Formation of larger cratons began in the late Archean 3 Proterozoic cratons start exhibiting modern style orgony mountain a Creation of the oldest surviving mountains i Wopmay Orogen 2 Ga 1 Orogeny eroded deformed remains of what was a mountain 2 Consists of deformed rocks since leveled by erosion 3 Distinct features igneous intrusion mm belt fold and thrust belt undeformed zone 4 Within the fold and thrust belt a Shallow water deposits Quartz sandstone and dolomite b Overlain by flysch turbidities c Shallow water deposits transitional stromatolites mudcracks d Give way to malasse nonmarine sediment 5 Proterozoic Wopmay Orogen similar to modern style orogeny 6 Means first continental crust was deformed Paleoproterozoic 1 Evidence suggests that Earth climate was much cooler 2 Ga a Glaciation evidence i Varves of Gowganda deposits some with dropstones 1 Proglacial ii Tillites found elsewhere 1 Global magnitude Mesoproterozoic 1 Stromatolites widespread by mid proterozoic a Mid proterozoic prokaryotic photosynthesisizing bacteria abundant i well represented in the Archean not abundant b Attributed to the expanse of continent and thus continental shelves c Leading to the proliferation diversification in shapes d Peak abundance and diversity 1 2 Ga 2 Eukaryotes protists of Archean lacked important features of advanced eukaryotes of Proterozoic 3 Advancement to modern eukaryote characteristics 4 Multicellular plantlike protists seaweed algae likely arose soon after the evolution of the fully developed eukaryotic cells a Oldest fossil multicellular algae 2 1 Ga b Acritarchs increasingly conspicuous singled celled algae 5 Photosynthesis by both prokaryotes and eukaryotes released large amounts a Oxygen built up likely triggered diversification of oxygen Earth System Shift 1 Atmospheric oxygen only 1 2 modern levels due to chemical sinks soaking up oxygen Proterozoic a Deposits of iron sulfide pyrite 2 3 Ga b Weakly oxidized BIF 1 9 Ga 2 Shift to abundant oxygen in atmosphere a Highly oxidized red beds after 1 9 Ga Neoproterozoic Biota 1 Through the mesoproterozoic well preserved Archean and Proterozoic algal mats indicate that grazing animals haven t yet evolved a Many Proterozoic surface beds formed at seafloor 2 Mesoproterozoic finely laminated sediment a Undisturbed not bioturbated 3 Neoproterozoic adaptive radiation animals a Evidence i Trace fossils burrows ii Soft bodied fossils worm like creatures on seafloor iii Skeletal fossils 4 First animal like single celled organisms and multicellular animal a Oldest animal like single celled organisms with skeletons 750 Ma b Oldest multicellular animal organism discovered 580 Ma a Oldest known undoubted adult animals preserved within the fossil 5 Ediacara fauna record i Animals lacked skeletons ii But preserved in these rocks iii Discovered in Australia but since then found all over the world b Characteristics i Non skeletal 1 Lived before predators otherwise wouldn t have abundance and diversity 2 Many similar to Cnidaria ii Some are imprints of soft bodied organisms c 570 Ma stationary benthic animals deep water preservation below phontic zone d 560 Ma mobile forms i Other fossils seafloor 1 Unknown simple disk structure attaching animal to 2 Animal related echinoderm different symmetry e Some fossils are similar to modern forms some don t have direct descendants i Animals resembling sea anemone ii Early arthropod iii An imprint of a mollusk like creature similar to snail print a Animals begin diversifying 560 Ma 20 Ma before end of 6 Origin of major animal groups neoproterozoic 7 Simple horizontal burrows a Evidence of worm like creatures 560 Ma 8 Skeletal fossils a Appeared very near end of Proterozoic Neoproterozoic Climate 1 Extensive Ice Ages a Known from geologic record of continental glaciers b Occurred three times i 700 750 Ma Sturtian ii 635 Ma Marinoan iii 580 Ma Gasker c Evidence of glaciation throughout the world equator i Snowball Earth hypothesis ii Sturian ice age and Marinoan ice age Earth System Shift 2 Sun s radiation output 6 lower than today 3 Continents clustered together at high altitudes 4 Combined triggered a positive feedback 5 Boulder tillites Marinoan SW Africa 6 Directly overlain by cap carbonates a Large biocarbonate crystals suggest biocarbonate in abundance 7 Evidence of abrupt climate change a Where did all the CO2 come from 8 CO2 build up below the ice covered oceans from underwater volcanic eruptions rapidly escape a Eventual partial melting or crevassing of sea ice cover allowed CO2 to 9 Oxidation of methane released from frozen methane hydrates on the seafloor Geology 1 Sizes of continents were changing during Proterozoic a Cratonic growth i Continent accretion 1 Microplate or island arc accretion ii Orogenic stabilization 1 Shelf sediment compressed and mm 2 Thickens and hardens crust b Evidence of continental rifting 2 Assembly of North America a Greenland and North America were combined as one landmass Laurentia i Core forming the NA craton Canadian shield b What lead to the formation of Laurentia i Amalgamation of Archean microcontinents ii Some Archean microcontinents separated by deep water sediments squeezed between igneous volcanic arcs iii Progressive classical continental accretion of terrenes continued to build Laurentia SW and EW iv Grenville orogeny last stage of Proterozoic expansion 1 Ga early Appalachian mtn formation 3 Failed rifting in NA a Failed rift 1 2 1 0 Ga i Volcanic belt through mid west ii Keweenawan basalts iii Failure reason unknown 4 First supercontinent Columbia 1 8 Ga a Partial breakup of Columbia 5 Rodinia fully assembled supercontinent 1 Ga a Around time of Grenville orogeny Laurentia united with other land b Larger size than future Pangaea c Probably located almost entirely south of the equator d Began to break apart 800 700 Ma i Post Keweenawan e Created Pacific Ocean f Previously failed rifts in western Laurentia were large depositional masses basins i Thick sequence of sediments 1 4 1 5 Ga along the passive western margin g Rifting likely released large quantities of nutrients into the oceans 6 Another supercontinent