The Hadean & Archean- Part I
Transcript of The Hadean & Archean- Part I
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The Hadean & Archean
Its the Earth Jim, but not as we know it.
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2
Questions
When and how did Earth and its moon come into being?
How did the core, mantle, crust form?
Where did Archean rocks form, and what is their nature?
When and why did large continents begin to form?
Where did life arise and what kinds of life existed at the end ofArchean time?
Why did relatively little free oxygen accumulate in Earthsatmosphere through Archean time?
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Precambrian Era
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Hadean,
ArcheanandProterozoic:
2500-4600Myrs
Era Age (Myrs) Epoch
0.01Holocene
1.8Pleistocene
5.3Pliocene
23.8Miocene
33.6 Oligocene
54.8Eocene
65Paleocene
144
206
248
290
323
354
417
443
490
543
2500
3800
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Eon
Proterozoic
Archean
Hadean
Period
Quaternary
Tertiary
Neogene
Paleocene
Mississippian
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Cretaceous
Jurassic
Age of the Earth 4600 Myrs (4.6 Byrs)Source: Geological Society of America (1999)
Geologic Time Scale
Devonian
Silurian
Ordivician
Cambrian
Triassic
Permian
Pennsylvanian
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Archean Divided into:
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2004 - Fred Sulahria
Hadean Earth
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Rocks Older than 2.5 Gyrs
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Hadean: What We Know
The Earth was a very different place!
But some major features of the Earth developed:
atmosphere (throughout Hadean)
oceans (water by 4.4 Gyr, stable oceans by 3.8 Gyr)
crust and continents (by 4.4-4.0 Gyr)
plate tectonics starts (about 4.0 Gyr)
magnetic field (about 4.5 Gyr)
life?
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Heavy Bombardment Period
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Bombardment may have led to a
Temporary Magma Ocean
~ 25 to 30 big impacts (few hundred to few thousand km in diameter) in the
last 200 million years of the major bombardment phase. A small meteorite
(50-60 km) would create an impact crater 1000 km across and 100 km deep!
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Magma Solidified into Early Crust
Komatiites
Ultramafic,
Dense,Uniform
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Atmospheric Formation
Hypothesis: Captured from Solar Nebula
Mostly Hydrogen and Helium
Would have been quickly lost. Earths gravity is not great enough to either
hold H or He at this temperature
If initially lost - where did the present
atmosphere come from?
1. Hydrous minerals (water-bearing) outgassed fromvolcanoes
2. Brought to Earth by comets
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Secondary Atmosphere - Outgassing
Initially Composed of:
Ammonia (NH3)
Hydrogen (H2) Carbon dioxide (CO2)
Methane (CH4)
Water vapor (H2O)
Nitrogen (N2)
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Similar to
Saturns
moon:
Titan
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The Faint Young Sun Paradox!
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One Reconstruction(Others have much more Carbon Dioxide in Hadean)
High carbon dioxide or methane solves the Faint Young Sun paradox due to
the Greenhouse Effect
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No Significant Oxygen!
Evidence:
No Rust Minerals
Pyrite and UraniniteConglomerates
(normally oxidize)
Extensive carbon-rich
rocks
Witwatersrand conglomerate, South Africa
(Middle Archean)
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Atmospheric EvolutionPrimary - Captured from Solar Nebula
- Mostly Hydrogen and Helium- Quickly Lost
Secondary - Formed by Outgassing by Volcanoes
Tertiary - Modified by Life (addition of Oxygen)
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Oceans
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Raining of the
Oceans
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Vaporization of the Oceans
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Hadean Oceans
Characteristics
Liquid Water existed at4.4 Gyrs
Ephemeral (periodically
vaporized)
Acidic (water + carbon
dioxide = carbonic acid)
Probably salty
Stabilized by end of
Hadean (about 3.8 Gyrs)
Evidence
Jack Hills Formation zircon crystalswith water inclusions
solar system evidence for heavy
bombardment and models
no limestones, atmospheric
models
acidic water (dissolves ions)
first limestones & sedimentary
rocks
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ContinentsFormationRequires PlateTectonics:
Subduction andmagmadifferentiationcreatesmore Felsic Crust
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Crustal Properties
Crust Density Composition Thickness Age
continental ~2.8 g/cm3 Felsic Thick:20-70 km
Old:up to4 Byrs
oceanic ~3.2 g/cm3
Mafic
Thin:
2-10 km
Young:
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The Aleutian Island Chain
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Seismic activity in the Aleutian Islands
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As Plates Move - Islands Accrete to
Form Larger Islands
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pillow lavas
http://www.pmel.noaa.gov/vents/nemo/explorer/concepts/pillow_lava.html
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Greenstones
Layered volcanics (pillow basalts; MORBs),conglomerates and greywackes (turbidites,
mudstones and shales formed from volcanic
sediments in deep water. More felsic at the
top. Green due to chlorite formed during
metamorphism.
Tonalites
(Granites)Felsic intrusions, slow
recycling of sedimentscreates less dense
materials that stabilize
the continental crust
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Continental Crust Forms
3.96 Billion Year Old Gneiss
What is the parent rock of a schist?
A Shale!
Where are shales formed?In the Ocean!
Therefore there had to be liquid water, an active
hydrologic system, i.e. rain, rivers,lakes etc.
LIFE?
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Continental Evolution
Up to 60% by the Proterozoic
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Proterozoic EonMaking the Modern World
Represents a change in crust and sediment formation.
Proterozoic sediments are more similar to Phanerozoic
sediments in that they are shallow water, beach, tidal
and deltaic, quartz-rich sandstones, shales and a very few
carbonates representing recycling of felsic crust instead
of simply volcanics and sediment from volcanic debris
E ( ) E hE P i d
Geologic Time Scale
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2500-543
Myrs
Era Age (Myrs) Epoch
0.01Holocene
1.8Pleistocene
5.3Pliocene
23.8Miocene
33.6
Oligocene
54.8Eocene
65Paleocene
144
206
248
290
323
354
417
443
490
543
2500
3800
P
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P
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Eon
Proterozoic
Archean
Hadean
Period
Quaternary
Tertiary
Neogene
Paleocene
Mississippian
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Cretaceous
Jurassic
Age of the Earth 4600 Myrs (4.6 Byrs)Source: Geological Society of America (1999)
Devonian
Silurian
Ordivician
Cambrian
Triassic
Permian
Pennsylvanian
2500 Myr
1600 Myr
1000 Myr
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Where Rocks of the Proterozoic are exposed
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Anatomy of a Continent
Orogenic
(Mobile) Belt
Basement Rock
North
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Western NorthAmerican Mobile
BeltMobile
Belt
North
American
Craton
Shield
Eastern North
American
Mobile Belt
Platform
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Precambrian Cratons:
Shields, Platforms and Mobile Belts
Uplifted Exposed Precambrian Rocks
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Canadian Shield
UpliftedBasement
Exposed Precambrian Rocks
Fold and thrust belt
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Cordillera
Western North
American Mobile
Belt, aka Orogenic
belt, i.e. Where
mostof themountains form
Fold and thrust belt
Laramide deformation and uplift
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Orogenies
= Mountian Building Events
Caused by:
1. Collision - Fold and Thrust Mountains
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Orogenies
= Mountian Building Events
Caused by:
2. Subduction - Volcanic (Arc) Mountains
A-2
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Basement
Provinces
of North
AmericaA.K.A.
The United Plates of
America
Archean Basement(>2.5 billion years)
Proterozoic Basement(2.5-0.5 billion years)
Mobile Belts
GF
A-2
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Northwest
Basement
GF
Wyoming Provenance
2.8-3.5 Gyrs old
Includes rocks found in
Beartooth Mtns and
Grand Teton National Park
Hearne Provenance
2.8-3.5 Gyrs old
Collision Zone:
Great Falls Tectonic Zone
(GF)
2.8 Gyrs ago
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The Beartooth valley: Precambrian rocks uplifted during the late
Cretaceous, glacially eroded in the Holocene, still eroding today
A-2
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Northwest
Basement
GF
Collision Zone:
Trans-Hudson Belt
1.9-1.8 Gyrs ago
Wyoming/Hearne collidewith Superior Provenance
By 1.8 Gyrs the basement
rock of NA was in place
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Continental Growth
Proterozoic
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Radioactive Heat Flow
Proterozoic
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WilsonCycle
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GrenvilleOrogeny
(The building
of Rodinia)
Archean Basement
Proterozoic Basement
Orogenic Belts
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Rocks of the Grenville Orogeny1.2-1.0 Gyrs
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RodiniaMotherland
Forms
1.2-1.0 Grs
Montana
New York
Belt Supergroup Montana
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Belt Supergroup, Montana
West Coast of Laurasia
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Mid
Continental
Rift
(1.3-1.0 Gyr)
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Origin of a
Failed Rift
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Continental Rift
Keweenawan Supergroup MI
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Keweenawan Supergroup, MIMesoproterozoic Rift Rocks
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Rodinia
Rifts(750 Myrs)
Montana
New York
Rifts to form the
(pre-Pacific)
Panthalassa
Ocean
Rifts to form the(pre-Atlantic)
Iapetus Ocean
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Rifting of
Rodinia
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Gondwana & Laurentia
About 500 Myr
At h i Ch
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Atmospheric ChangesOxygen Increases: Carbon Dioxide Decreases
Proterozoic
Thanks to
BIFs
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BIF s
(3.5-1.8 Gyrs)
Banded Iron Formation
92% Between
2.5-2.0 Gyrs
The rest in the
Neopropterozoic
~ 600-700 Mya
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Carol LakeIron Mine,
Canada
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Red Beds
< 1.8 Gyrs
After iron in the
ocean was used
up, oxygen started
to accumulate in
the atmosphere.
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Oxygen Buildupoccurs at
(the Same Time?)
as First
Eukaryotes
Appear
Atmospheric Changes:
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Atmospheric Changes:
UV Protection
Where Did All the Atmospheric
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Where Did All the Atmospheric
Carbon Dioxide Go?
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Carbon Storage
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The Carbon Thermostat,i.e the greenhouse effectCarbon burial as carbonates (limestones, dolomites and organic matter) resulted in
decreases in atmospheric carbon dioxide, which made it possible for
Paleoproterozoic (2.2 Gyr)
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Paleoproterozoic (2.2 Gyr)
Gowganda Fm, Canada
Tillite
VarvesThe First Ice Age
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Major
Ice Agesin Earth History
1
2
3
4
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Neoproterozoic (Varangian)
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Ice Age (800-600 Myr)
Tillite
Carbonates &
Ironstones
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Neoproterozoic
Snowball Earth
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Snowball Earth
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Snowball Earth
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Why Banded
IronFormations?
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Ice Age Ends at the
Around the Same
Time the FirstMulti-Celled
Animals Appear
Coincidence or not?