The Hadean & Archean- Part I

8/6/2019 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

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543

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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

r

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c

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m

b

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P

h

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z

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Eon

Proterozoic

Archean

Hadean

Period

Quaternary

Tertiary

Neogene

Paleocene

Mississippian

C

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z

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ic

M

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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

O i


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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

5


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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?

Documents

The Hadean & Archean- Part I