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Precambrian

Precambrian. Life. 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 Atmosphere. Primitive atmosphere He, H  in H2O vapor

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Precambrian

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  1. Precambrian Life

  2. 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 Atmosphere

  3. Primitive atmosphere He, H  in H2O vapor 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 O2-breathing organisms Little free O2 in atmosphere until evolution of photosynthetic organisms Some oxygen by photochemical disassociation Reducing environment changed to oxygenation one Earth’s Early Atmosphere

  4. Evidence for oxygen production and accumulation in Earth’s atmosphere Banded Iron Formations (BIF’s) Red Beds Precambrian Atmosphere

  5. 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 Banded Iron Formations (BIF’s) PreCambrian BIFs

  6. Photosynthesis produced oxygen Origin of BIF’s • Combined with Fe to produce “rusty rain” in ocean

  7. 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 Red Beds

  8. Origin of Red Beds ferric iron oxides: red beds • Red beds formed after all reduced iron in ocean had been oxidized

  9. Prokaryotes Eukaryotes Ediacaran Fauna Where did the O2 come from?

  10. 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 Protein Synthesis

  11. 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 Silica gel (volcanism) trapped organisms Fig tree chert S. Africa = 3.1 Ga Stromatolite NW Australia = 3.5 Ga 3.85 in Greenland Earliest Organisms 3.5 Ga Stromatolite Modern Stromatolite

  12. Cyanobacteria Blue-green algae Single celled, lack nucleus Contain DNA, but no membrane-bound organelles Undergo photosynthesis Archean - Prokaryotes

  13. Prokaryotes 3.3-3.5 Ga Prokaryote Warrawoona Group, W. Australia 3.3-3.5 Ga Prokaryote Warrawoona Group, W. Australia

  14. 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 Archean Eukaryotes

  15. Eukaryotes Microfossils, Gunflint Fm, Canada 700-800 Ma Microfossils, Beckspring Dolomite, California

  16. Common Proterozoic Eukaryotes

  17. 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

  18. Metaphytes and Metazoans Possible multi-cellular algae, Little Belt Mtns., Montana • 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

  19. 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 Ediacaran Fauna

  20. Reconstruction Ediacaran Environment

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