The Archaen Flashcards
What event/period marked the beginning of the Archean eon?
The Late Heavy Bombardment
Time period of the Archean eon:
3.8-2.5 Ga
lasted 1.3 billion years
What eon did life originate in?
Archaen
3 Important events of the Archaen:
End of Late Heavy Bombardment, origin of life, first accretion of continents.
Archean Tectonics were different from current tectonics in what ways?
More volcanism/abundant magma, faster moving plates, more heat in system, smaller cratons
Where are Archean rocks typically found?
exposed shield area of cratons
How much of exposed Precambrian rock is Archean (instead of Proterozoic)?
22%
What geologic features do not appear in Archean rock that normally appears in sedimentary rock?
Epicontinental seas, carbonate rocks, broad continental shelves
Archean rock types:
Greenstone 20%, granite-gneiss complexes 80%
what is a greenstone association?
Metamorphosed underwater volcanics and sediment derived from weathering of volcanics, usually in a syncline formation with 3 layers
What do greenstone belts represent?
- successive phases of cratonic accretion
- Suturing island arcs together to form early cratons
- A stage before Proterozoic craton-craton accretion
How old is Canadian continental crust?
4.04 Ga
How big are cratons at the end of the Archean relative to their current size?
30-40%
What was the atmosphere of the Archean like?
very low oxygen, lots of acidic rain from volcanism
What is Abiogenesis?
the formation of life from lifelessness
What made abiogenesis possible in the Archean that is now not the case? (why can life not evolve from lifelessness now?)
Very low free oxygen in the atmosphere during the Archean made abiogenesis possible.
How long ago is it believed that life first arose?
4 billion years approximately… end of hadean or early Archean.
lineages of individuals that evolve through descent with modification describes?
life
What were the first super continents?
valbara and ur
What was Archean life probably like?
prokaryotic, no cellular respiration/anaerobic, probably chemo autotrophic
When did eukaryotes first appear?
2.7 Ga in chemical trace fossils
What created the first oxygen-rich atmosphere?
Cyanobacteria evolved a non-cyclic photosynthesis that released oxygen.
How old are stromatolites?
3.45 Ga
What is the RNA world hypothesis?
life first transmitted genetic information with RNA that later evolved to DNA.
