The Formation of Earth's Core, Mantle, and Atmosphere: A Geological Timeline - Prof. Thoma, Study notes of Geology

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GEOL 102: Historical Geology Exam 2 Review The Time Scale (for Exam 2: You are not responsible for the numbers): Eon Era Period Range (Ma) Phanerozoic Paleozoic Permian 299-251 Carboniferous 359-299 Pennsylvanian 318-299 Mississippian 359-318 Devonian 416-359 Silurian 444-416 Ordovician 488-444 Cambrian 542-488 Proterozoic Neoproterozoic Ediacaran 630-542 Cryogenian 850-630 Tonian 1000-850 Mesoproterozoic Stenian 1200-1000 Ectasian 1400-1200 Calymmian 1600-1400 Paleoproterozoic Statherian 1800-1600 Orosirian 2050-1800 Rhyacian 2300-2050 Siderian 2500-2300 Archean Neoarchean 2800-2500 Mesoarchean 3200-2800 Paleoarchean 3600-3200 Eoarchean c. 4030-3600 Hadean 4560-c. 4030 Hadean Eon Precambrian definition Hadean definition Craton = Platform + Shield; Orogen Hadean events: • Formation of proto-Earth by accretion of planetesimals (ices, organics, silicates, metals) • The Iron Catastrophe: energy from collisions & radioactive decay & gravity differentiates proto-Earth into Core (metals), Mantle (silicates), and Atmosphere (gases) o Primordial atmosphere: H, He, limited amounts of water vapor & other gases; lost due to solar wind, low gravity, energy from impacts (especially Theia) • Collision with Mars-sized Theia produces Earth & Moon o Earth’s mantle melts into Magma Ocean o When cools below boiling point of water, actual water oceans form o Reducing Atmosphere: carbon dioxide, methane, ammonia, water vapor, nitrogen; formed from volatiles degassing out of mantle • Crust forms from partial melting of mantle in presence of water. Originally all mafic, but continental-type lithologies from additional partial melting by 4.40 Ga • High speed tectonics Archean Eon Late Heavy Bombardment: increased rate of impacts from 4.1-3.8 Ga Archean geology: Granitoid-Greenstone complexes Komatiites Banded Iron Formations Cratonic Complexes Difference between Archean and post-Archean tectonics, atmosphere, etc.: detrital uraninite & pyrite Possible presence of continent Ur by 4.2 Ga Evidence for Archean life: • Fractionated carbon ~3.8 Ga • Microfossils in chert possible 3.5 Ga, definite 3.4 Ga • Stromatolites 3.4 Ga: ?cyanobacteria, or maybe earlier non-aerobic phototrophs • Abiogenesis by 3.4 (or 3.8) Ga o Simple building blocks amino acids biological polymers competition for space/resources accumulation of traits of simple cells • Biofilms: dominant way of life from Archean through Proterozoic • LUCA: Last Universal Common Ancestor, by 3.4 Ga • Prokaryotes (archaeans & bacteria), many extremophiles Oldest glaciers at 2.9 Ga Sterols (compounds made by eukaryotes) by 2.7 Ga Proterozoic Eon Shift to modern tectonism and orogenic belts (2.95 Ga in southern Africa, later elsewhere) Kenoran Orogeny (2.5 Ga) One of the oldest known, evidenced by granitic intrusions into Archean rocks, Superior Province in Canada Wopmay (2.0 Ga) Oldest for which good structural & lithological evidence is known, Slave Province in Canada Great Oxidation Event: • Phase I: 2.7-2.4 Ga, increased level of oxygen due to cyanobacteria sucked up by iron in water, major BIF deposition • Phase II: 2.4-2.0 Ga, oxygen levels climb in atmosphere; reducing atmosphere is oxidized (methane, ammonia, etc. broken down) o The Nitrogen-Oxygen Atmosphere • First oxidized terrestrial redbeds • Last detrital pyrite & uraninite ~2.3 Ga; last BIFs around 1.9-1.8 Ga • Huronian Glaciations (at least 3 pulses between 2.45 & 2.2 Ga; loss of greenhouse methane cooled world Craton assembly: • Arctica: 2.5 Ga; Northern & central Canadian, Greenland, Siberian cratons; Maybe the Kenoran Orogeny is a record of this? First trees and increased land plants leads to meandering streams, increased oxygen levels, first soils (lowered carbon dioxide leads to climate change) Major mass extinction destroys tabulate-stromatoporoid reef community; extinction of stromatoporoids & “ostracoderms”; loss of most tabulates, rugosans, primitive echinoderms, placoderms, “acritarchs”, brachiopods, conodonts, ammonoids (latter three all rebound!) Paleozoic Era: Carboniferous (C), Mississippian (M) & Pennsylvanian (|P) Shift from calcite to aragonite seas; Reefs rare, but crinoid meadows common Major new M fossil groups: fusulinid forams; sharks & ray-fins diversify Antler Orogeny [First part of Cordilleran system] (M): collision of Antler Island Arc & western North America Variscan Orogeny (Late M): Beginning of closure of Rheic Ocean, Iberia (then part of Gondwana) collides with French part of Euramerica; sometimes called “Hercynian Orogeny” Alleghanian Orogeny [Third and final part of Appalachian system] (M-|P): Gondwana collides with eastern North America Ouachitan Orogeny (|P): Collision between American Gulf Coast & Gondwana Ancestral Rockies Orogeny [Second part of Cordilleran system] (|P): vertical displacement in response to Ouachitan Uralian Orogeny (|P-P): Siberia + Euramerica = Laurussia “Romer’s Gap”: low levels of diversification of tetrapods and terrestrial arthropods in M, possibly because of low oxygen levels Coal Swamps in Northern Hemisphere; Cyclothems/coal measures driven by glacioeustatic transgression-regression cycles (very rapid), only in north because of shallower topography Coal Swamp vegetation: scale trees (lycopods, giant clubmosses; in wet lands); segmented trees (Calamites, giant horsetail ferns), shoots allow them to propagate into drier land; “gymnosperms” (primitive seed plants) successful in very dry land, including seed ferns, cordaites, conifers. Scale trees die off at end of C, segmented trees in early P, cordaites until P/Tr extinction. Continued drop in CO2 (down to similar levels to pre-industrial modern) and all-time high of O2 due to coal deposits; peak of Gondwanan glaciation Major new terrestrial animals: Arthropleurids (top herbivores); insects (fixed wings in early |P, folded wing by late |P); giant arthropods in general; tetrapods (fully terrestrial as adults) (including first amniotes in late |P) Paleozoic Era: Permian (P) Assembly of Pangaea; Panthalassa Ocean & Paleotethys & Tethys Oceans Development of continental climates, widespread deserts, draining of coal swamps Permian reefs (brachiopods, bryozoans, sponges, algae) Glossopteris flora around Gondwanan glacial region Major P land animals: Amphibian-grade tetrapods diversify; amniotes (originated in |P) diverged into synapsids and reptiles; synapsids (incl. therapsids) dominant terrestrial vertebrates; Sonoman Orogeny [Third part of Cordilleran system] (latest P-early Tr) Sonomia collides with western North America Siberian Traps volcanism Permian/Triassic Mass Extinctions: • Greatest in Phanerozoic (two phases (Guadalupian & P/Tr), together killing off 95% of marine species) • Total extinction of trilobites, rugose & tabulate corals, lacy (& most stony) bryozoans, blastoids, graptolites, fusulinids, eurypterids, placoderms • Extinction of all but a few genera each of brachiopods, crinoids, ammonoids, conodonts, therapsids • Extinction of many insect groups • Associated with Siberian Traps, massive carbon isotope shifts, severe anoxia and hypercapnia (high CO2) in sea and atmosphere