Precambrian
(Chapters 9 and 10)
Precambrian (Cryptozoic) 4.2 - .57 byrs
Archean 4.2 -2.5 byrs.
Proterozoic 2.5 - .57 byrs.
Eocambrian .7 - .57 byrs
Precambrian Shields
Fig. 9.4
Precambrian Fossils
Stromatolites
oldest 3.5 byrs.
common mid-late Precambrian
cyanobacteria (blue green algae)
Fig Tree Group
South Africa
- 4 byrs.
prokaryotes - bacteria, cyanobacteria
Bitter Springs Fm.
Central Australia
- 9 byrs
eukaryotes
Evolution of Life, Hydrosphere & Atmosphere
4.6 byrs
Origin of the Earth
outgassing (fig. 9.15)
anoxic
no ozone layer
low pH HCO3-
?organic soup?
?3.9 byrs
heterotroph
fermentation
C6H12O6 --- 2CO2 + 2C2H5OH + energy
autotroph
methanogens
H2 + CO2 --- CH4
anaerobic
3.5 byrs
anaerobic photosynthesis
6CO2 + 6H2O --sunlight---- C6H12O6 + 6O2
3.2 byrs
Evidence in the Rocks
4.3-2.0 byrs
detrital pyrite & uraninite
lack of O2 in the atmosphere
3.0 - 2.0 byrs.
banded iron formations
O2 in the oceans
2.0 byrs
red beds
O2 in the atmosphere
Evolution of Lithosphere
Archean
different style of tectonics
high heat flow
thin crust (fig. 9.14)
Granite-gneiss terrains
metamorphosed granite
gabbroic intrusions
ancient continental crust
Greenstone belts
volcanic-sedimentary basins
volcanics ultramafic to felsic
komatiite - ultramafic volcanic
sediments
Proterozoic
Quartzarenite - carbonate - Shale assemblage
continental shelf deposits
banded iron formation
anorogenic igneous activity (fig. 10.5)
granite-rhyolite provinces
anorthosite 1.4 - 1.5 byrs
ophiolite
0 byrs. Jormua Complex, Finland
?2.65 byrs. Wyoming
Wompmay Orogeny
NW Canada
1st complete Wilson Cycle
- 1 - 1.8 byrs.
Fig. 10.4
last updated 4-21-98
All original material copyright (c) 1998 by Annabelle Foos. All rights reserved.