Biography of 13_00.jpg
Earth
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Methods:
Locating & studying ancient orogens
Recognizing continental growth and development
Recognizing past depositional environments
Recognizing past changes in sea level
Recognizing past continental positions (pmag, marine magnetic
anamolies)
Recognizing past climates
Recognizing life evolution
“outgassing” of mantle to form early, dense atmosphere
Hadean Eon: 4.57 - 3.8 Ga
Accretion of planetesimals
Partial melting and iron catastrophe (first step in
differentation)
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Collision of Mars-sized proto planet with earth
to form Moon
Some solid rock by 4.4 Ga; age of
zircon and oxygen isotopes suggest cool
enough for water
Oldest whole rock gneiss 4.03
Ga
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Formation of early ocean during Hadean - timing poorly constrained
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80% of continental crust
formed during Archean
Archean Eon 3.8-2.5 Ga
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Archean cratons: five main rock types: gneiss,
greenstone,
granite, graywacke, chert
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Rivers flowed over early unvegetated continents,
carrying sediments and salt to sea
Spherical bacteria found in
3.2 Ga old chert in South
America
Isotopic signature suggests life on earth by 3.5 Ga
(elevated C12 relative to C13 in carbon-rich
sediments)
First undisputed life forms by 3.2 Ga
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Stromatolite 3.2 Ga old - mats formed by cyanobacteria secreting
mucous-like substance that traps sediment
And…..photosynthetic organisms by 2.7 Ga!
Modern Stromatolites, Shark Bay, western Australia
http://en.wikipedia.org/wiki/Image:Stromatolites_in_Sharkbay.jpg
http://facweb.bhc.edu/academics/science/harwoodr/rhweb/austra98/Aust12.jpg
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Proterozoic Eon: 2.5 Ga to 542 million years
Most large cratons formed by 1.8 Ga
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Banded iron formation - jasper (red chert) + hematite (iron oxide)
- all formed before 1.88 Ga in iron rich oceans (which were then oxygen poor)
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“Dickinsonia” Ediacaran fauna of the late Proterozic seas
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Phanerozoic Eon: “visible life” - 542 Ma to present
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Ordovician Period
Taconic orogen
Avalon
Epicontinental seas
Cambrian explosion of life
The Devonian Period
Acadian orogen
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Middle Ordovician
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Cambrian life - trilobites & nautiloids
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Sequence
stratigraphy
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Devonian Period Acadian orogeny (to N in
Northern Europe, the
Caledonian orogeny)
Iapetus Ocean
subducted
Erosion of TaconicAcadian orogens
supplied sediments to
SW US
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Late Devonian
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decompressor
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Alleghenian orogeny - felt mostly in SE US collision of Gondwana with Laurentia
Late Pennsylvanian
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decompressor
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Cross-section of the Alleghenian orogen
of Carboniferous and Permian times
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Lots of shallow marine coal swamps during the Carboniferous Period
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Addition of exotic
terranes to western
North America from
Jurassic to Cretaceous
Periods
Break up of Pangea - late Triassic into Jurassic Periods
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Permian extinction event gave rise to new
Triassic life forms - dinosaurs
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Jurassic Period - age of the dinosaurs
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Green house
conditions - interior
seaways superplumes - high
mid-ocean ridge
activity - increas in
CO2
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End of Cretaceous period
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