Archean & Proterozoic Life

SOME TERMINOLOGY

• PROKARYOTE - NO internal organelles or membrane-bound nucleus with chromosomes
• EUKARYOTE - HAVE internal organelles (chloroplasts & mitochondria) & membrane-bound nucleus with chromosomes
• ANAEROBE - cannot survive in an environment with free oxygen
• AEROBE - can survive in an environment with free oxygen
• HETEROTROPH - cannot synthesize food
• AUTOTROPH - can synthesize food by fixing Carbon
• CHEMOSYNTHESIS - use chemical energy to fix Carbon
• PHOTOSYNTHESIS - use sunlight to fix Carbon

FIRST ORGANISMS

• HETEROTROPHIC ANAEROBIC PROKARYOTES (PROBABLY)
  • metabolized pre-existing organic molecules by fermentation or methanogenesis

C6H12O6 -> 2 C2H5OH + 2 CO2 + energy (2 units)

(glucose) -> (ethanol)

• modern Heterotrophs are mostly Aerobic Eukaryotes that metabolize pre-existing organic molecules by oxidation

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy (36 units)

FIRST AUTOTROPHS

• CHEMOSYNTHETIC ANAEROBES (PROBABLY)
  • used heat energy from MOR hot springs

FIRST PHOTOSYNTHETIC AUTOTROPHS

• ANAEROBIC BACTERIA (PROBABLY)
  • like those now found only in restricted environments [anaerobic hot springs in Yellowstone Park]

6 CO2 + 6 H2S + energy -> C6H12O6 + 6 S (no free oxygen)

• as old as oldest continental crust (probably)
  • CARBON SPHERES IN 3.8 BY OLD ROCKS OF GREENLAND

SECOND PHOTOSYNTHETIC AUTOTROPHS

• AEROBIC CYANOBACTERIA (BLUE-GREEN ALGAE) (PROBABLY)

6 CO2 + 6 H2O + energy -> C6H12O6 + 6 O2 (lots of free oxygen)

• O2 initially produced by cyanobacteria reacted chemically with previously dissolved (Fe+2) iron to form Banded Iron Formations (BIFs) & did not accumulate in the atmosphere
• ~2 billion years ago the dissolved iron reservoir was exhausted & the atmosphere began to be "polluted" by O2
  • ANAEROBIC ORGANISMS DRIVEN BELOW THE SURFACE
• modern Photosynthetic Autotrophs are mostly Aerobic Eukaryotes

ARCHEAN FOSSIL RECORD

• ARCHEAN FOSSILS ARE NOT ABUNDANT, OCCURRING IN ONLY A FEW PLACES, & CONSIST OF ONLY 2 TYPES - MICROFOSSILS & STROMATOLITES
  • Microfossils - prokaryote bacteria & cyanobacteria only
    • WARRAWOONA GROUP - 3.5-3.4 BY OLD (WESTERN AUSTRALIA) - PRIMITIVE BACTERIA & PRIMITIVE FILAMENTOUS CYANOBACTERIA
    • FIG TREE GROUP - 3.4 BY OLD (SOUTH AFRICA) - PRIMITIVE BACTERIA & UNICELLULAR CYANOBACTERIA
  • Stromatolites - formed by photosynthetic cyanobacteria & presently are restricted to stressed environments; during the Precambrian occurred in many environments
    • POSSIBLY IN WARRAWOONA GROUP (3.5-3.4 BY)
    • PONGOLA SUPERGROUP & BULAWAYAN GROUP - 3.1-2.8 BY OLD (SOUTHERN AFRICA)
    • STROMATOLITES ARE NOT ABUNDANT UNTIL THE EARLY PROTEROZOIC

MAJOR PROTEROZOIC LIFE EVENTS

• EVOLUTION OF EUKARYOTES IN THE EARLY PROTEROZOIC
  • Eukaryotes are thought to have developed from symbiotic relationship between previously-independent prokaryotes
    • EUKARYOTES ARE LARGER THAN PROKARYOTES
  • Organization of DNA into chromosomes in nucleus allowed development of sexual reproduction & the rate of organic evolution increased
  • Eukaryotes did not evolve until the atmospheric O2 began to accumulate
    • ALL EUKARYOTES ARE AEROBES
• EVOLUTION OF MULTICELLED ORGANISMS
  • multicelled algae - Middle Proterozoic
  • multicelled animals - Late Proterozoic

EARLY PROTEROZOIC FOSSIL RECORD

• EARLY PROTEROZOIC FOSSILS ARE NOT ABUNDANT, OCCURRING IN ONLY A FEW PLACES, & CONSIST OF ONLY 2 TYPES - MICROFOSSILS & STROMATOLITES, LIKE THE ARCHEAN
  • Microfossils - prokaryote bacteria & cyanobacteria only until about 1.8 BY
    • GUNFLINT CHERT - 2.1-1.8 BY OLD (NORTH AMERICA) - DIVERSE ADVANCED BACTERIA & FILAMENTOUS CYANOBACTERIA
    • FORTESCUE GROUP - 1.8 BY OLD (WESTERN AUSTRALIA) - DIVERSE ADVANCED BACTERIA & FILAMENTOUS CYANOBACTERIA
  • Microfossils - eukaryotes evolved about 1.8 BY
    • INIDICATED BY LARGER SIZE, THICKER CELL WALLS, & CHEMICAL COMPOUNDS UNIQUE TO EUKARYOTES
  • Stromatolites become abundant in the Early Proterozoic
    • FORTESCUE GROUP - 1.8 BY OLD (WESTERN AUSTRALIA)

MIDDLE PROTEROZOIC FOSSIL RECORD

• MULTICELLULAR ALGAE EVOLVED; GREAT DIVERSIFICATION OF LIFE
  • Microfossils - first appearance of acritarchs (cysts of planktonic eukaryotic algae)
  • Multicellular organisms - multicellular algae (carbonaceous imprints)
    • POSSIBLY IN LITTLE BELT MOUNTAINS - 1.4 BY OLD (MONTANA)
    • WIDESPREAD IN SPITZBERGEN, CHINA, INDIA, & CANADA - 1.2-0.7 BY OLD

LATE PROTEROZOIC FOSSIL RECORD (see Precambrian-Paleozoic Boundary notes)

• MULTICELLULAR ANIMALS (EDIACARA FAUNA) EVOLVED <600 MY AGO
• STROMATOLITES WERE VERY ABUNDANT
  • Restricted to hypersaline environments during the Phanerozoic

Study Questions

1. What are the differences between heterotrophs & autotrophs, and anaerobes & aerobes?

2. What was the probable nature of the earliest organisms?

3. What were the probable steps from anaerobic heterotrophs to aerobic photosynthetic autotrophs?

4. What were the changes in the Earth's atmosphere & rocks resulting from evolution of photosynthetic cyanobacteria?

5. What are the differences between prokaryotes & eukaryotes (the differences in their internal structure)?

6. How are eukaryotes thought to have evolved?

7. What was the effect the evolution of eukaryotes on the rate of organic evolution?

8. Summarize the general characteristics of the Archean and Early & Middle Proterozoic fossil records (the age & location of and the types of fossils in the important rock units containing these fossil records).

9. What are the differences between the Early Proterozoic & the Archean fossil record.

10. What were the major organic evolutionary events of the Middle Proterozoic.

11. When did eukaryotes evolve & what is the evidence for this event?

12. When did multicellular algae evolve?

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