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BIO211 oct 12

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Jessica Hawthorn

BIO211 Oct 12 th The “Precambrian” Hadean - originally designated as time before oldest known rocks (at the time, 3.8 billion years ago), but now older rocks are known and included in the Hadean Archean Eon Proterozoic Eon Precambrian Craton - craton: large non-deformed portions of very old continents, usually of Precambrian age - Canadian shield: Precambrian craton exporsed at surface - high heat flow produced small, thinner continents Greenstone Belts - continental accretion o deep water sediments accreted to continent o marine sediments form wedge between continental masses o weakly metamorphosed from igneous mafic and sedimentary rocks o nested within high-grade felsic metamorphoc rocks o abundant chlorite Banded Iron Formations - Chert interbedded with sediments rich in iron - formed in low O2 marine environments - stopped forming 1.9 Ga (billion years) ago Early Life - filamentous bacteria present ~3.5 billion years ago - stromatolites: structures built by cyanobacteria; 3.5 billion years ago-present - biomarkers for eukaryotic cells o steranes 2.7 billion years old Artificial Life? - Miller and Urey (1953) produced nearly all amino acids found in proteins o modeled primitive atmosphere o added “lightning” spark o included O2 - showed that amino acids form easily Mid-Ocean Ridges - high heat  areas around ridges offer wide range of temperatures o organic compounds readily dissolve in warm water - chemosynthetic organisms o hydrogen oxidation o sulfur reduction o methan production - protection from UV radiation and oxygen - phosphorus and metals present - contain clays Proterozoic Orogenesis - formation of large cratons and earliest modern-style orogeny  Wopmay orogen: 2 billion years ago
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