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Precambrian Life Earth’s Atmosphere • Today’s atmosphere and hydrosphere is different than Precambrian • Today’s atmosphere: – Nitrogen (N2) – Abundant free oxygen (O2) – Water vapor (H2O) – Ozone (O3) Earth’s Early Atmosphere • Primitive atmosphere – He, H Blown away (no magnetosphere) or lost to space (not enough gravity) – O2 in H2O & CO2 – C in CO2 – But deficient in O2 & rich in CO2 • Gases from cooling magma – Simple gases – methane (CH4) & ammonia (NH3) • Atmosphere not conducive to O2breathing organisms • Little free O2 in atmosphere until evolution of photosynthetic organisms – Some oxygen by photochemical disassociation – Reducing environment changed to oxygenation one Precambrian Atmosphere • Evidence for oxygen production and accumulation in Earth’s atmosphere – Banded Iron Formations (BIF’s) – Red Beds Banded Iron Formations (BIF’s) • Occur in rock record about 3.2 Ga—most at2.0-2.5 Ga • Formed in oceans • Consist of chert (SiO2) & red bands – Red Bands rich in iron oxides Fe2O3, Fe3O4 • Record major oxygenation event PreCambrian BIFs Origin of BIF’s • Photosynthesis produced oxygen – Combined with Fe to produce “rusty rain” in ocean Red Beds • Similar to BIF’s, but . . – Terrestrial formations – Lower in Fe concentration • Occur in rock record about 2 Ga – Atmosphere at this time only had 1-2% O2 • Indicate O2 present in atmosphere to “rust” sediments – O & O3 more effective oxidizing agents Origin of Red Beds ferric iron oxides: red beds • Red beds formed after all reduced iron in ocean had been oxidized Where did the O2 come from? • Prokaryotes • Eukaryotes • Ediacaran Fauna Protein Synthesis • S. Miller, chemist (1953) • Reconstructed “early atmosphere” – Mixed methane, ammonia, H2 and H2O vapor – Applied electrical charges produced amino acids Heat, UV radiation, sunlight, radioactivity can do same • Process called abiotic synthesis • Today, only organisms produce amino acids – Amino acids + organic molecules = protein Earliest Organisms • Must have had anaerobic (no O2) heterotrophs – Used organic soup for food • Free O2 lethal to anaerobic heterotrophs – Need to adjust to ↑ O2 • Cherts important 3.5 Ga Stromatolite – Silica gel (volcanism) trapped organisms • Fig tree chert – S. Africa = 3.1 Ga • Stromatolite – NW Australia = 3.5 Ga • 3.85 in Greenland Modern Stromatolite Archean - Prokaryotes • bacteria – Single celled, lack nucleus • Contain DNA, but no membrane-bound organelles • Undergo photosynthesis Prokaryotes 3.3-3.53.3-3.5 Ga Prokaryote Ga Prokaryote WarrawoonaWarrawoona Group, W. Australia Group, W. Australia Archean Eukaryotes • Contain nucleus, DNA and are larger • Membrane-bound organelles • Fig tree has chemical indicators of life – Pristane/phytanes Chlorophyll products – C-12 & C-13 Used by photosynthesizing organisms Eukaryotes Microfossils, Gunflint Fm, Canada 700-800 Ma Microfossils, Beckspring Dolomite, California Common Proterozoic Eukaryotes Metaphytes and Metazoans • 3.5-0.9 Ga small organism – Single cell or few cells attached • Next important evolutionary step – Combination of cells to form macroscopic organism Metaphytes and Metazoans • Metaphytes (plants) – First plants = algae – May have multi-cellular algae • Metazoans (animals) – First evidence is trace fossils – Found in late Precambrian – Montana, Canada – Made by large organism Possible multi-cellular algae, Little Belt Mtns., Montana Ediacaran Fauna • Soft-bodied fossils in SS, S. Australia – 1.0”-2.0”, some a few feet – Heterotrophs; previously all autotrophs Depend on outside food source – Multi-celled organisms Led to specialized cells Led to organs – Evidence of systems in organisms Reconstruction Ediacaran Environment