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 Vendian-Cambrian Life 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?