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  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 O 2 - breathing 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 at 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 O 2 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 O 2 ) 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 3.5 Ga Stromatolite Modern Stromatolite

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

Prokaryotes Ga Prokaryote Warrawoona Group, W. Australia Ga Prokaryote Warrawoona 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 Ma Microfossils, Beckspring Dolomite, California

Common Proterozoic Eukaryotes

Metaphytes and Metazoans 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) Metazoans (animals) – First plants = algae – May have multi-cellular algae – 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