Archean
• Eoarchean: 3.8 - 3.6 Ga
Archean Oceans
Orin Robinson
– oldest known terrestrial rocks
– possible beginning of formation of first
supercontinent
• believed to have existed as far back as 3.6 Ga
– debatable geochemical evidence for life
• not widely accepted
Archean
Archean
• Paleoarchean: 3.6 3.2 Ga
• Mesoarchean: 3.2 2.8 Ga
– evidence for the first
stromatolites
– formation of the first
stable crusts
– first widely accepted
fossil evidence of life
– banded iron formations
http://www.uwsp.edu/geo/faculty/hefferan/Geol106/
CLASS3/ARCHEAN%20LIFE.htm
• still being debated
www.amnh.org
http://www.wmnh.com/wmel0000.htm
Archean
• Neoarchean: 2.8 2.5 Ga
– first large
continental shields
Archean Tectonics
• Interior of the Earth
was 3x hotter than
today
• Rapid formation and
recycling of oceanic
crusts
• Many small plates and
volcanic islands
http://www.cotf.edu/ete/modules/msese/earthsysflr/cambrian.html
http://www.uwsp.edu/geo/faculty/hefferan/Geol106/CLASS3/archean_rocks.htm
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Origins of Life
Archean Atmosphere
Miller-Urey Experiment
• N2, CO2, HCl, SO2,
CH4, NO2, NH3
• No O2 or Ozone
• Oceans probably had
similar composition
http://www.kennislink.nl
/upload/115265_962_10
91536575830millerurey.jpg
http://www.windows.ucar.edu/
tour/link=/cool_stuff/tour_Archean_4.html
Miller-Urey Experiment
• 2% of the C in the
experiment was in the
form of amino acids
• Drying and rewetting
of organic compounds
in these experiments
produced membranes
and simple proteins
• This lead scientists to
believe that life had to
arise in shallow pools
Origins of Life
• Hydrothermal vents
provide buildingblocks for life
• Provide energy source
in the form of sulfur
and sulfur compounds
• Protects newly formed
organic compounds
from UV radiation
http://members.iinet.net.au/~drage/images
/ume.jpg
Life in Shallow Archean Pools
• Life would not have survived in shallow
pools in the Archean
– UV radiation would have destroyed any organic
compounds that formed
• No protection by ozone
Origins of Life
• Stromatolites then
proliferated
• Produce O2
– Banded Iron Formations
• Began changing the
atmosphere
• Oxygen started
accululating in the
atmosphere by the early
Proterozoic (~2.5 Ga)
http://www.uwsp.edu/geo/faculty/hefferan/Geol106/
CLASS3/ARCHEAN%20LIFE.htm
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