Download PreCambrian Life

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