The Hadean and Archean
Instructor: Dr. Douglas W. Haywick

Evolution 1: the origins of life
1 ) The Earth 3.9 billion years ago
2) The first Organic Reactions?
3) The First Life Forms
Evolution 2: How it works
1) Definition of Evolution
2) Darwin's law of natural selection ( gradualism, punctuated equilibria )
3) examples of evolutionary development
(Web Lectures 14 & 15)

Today:
N
2
= 78%; O
2
=21%; Ar=1%;
H
2
O=variable; CO
2
=0.03%
4.1 GA:
N
2
; HCl; SO
2
; CO
2
; CH
4
; NH
3
; NO
2
; H
2
O
NO…. O
2
How do we know?

Volcanic eruptions

Venus

4.1 GA:
N
2
; HCl; SO
2
; CO
2
; CH
4
; NH
3
; NO
2
; H
2
O

The Western Australia beasties were very “simple” single celled organisms like today’s bacteria

1953: two very clever biochemists ( Stanley Miller and Harold Urey ) conducted some experiments that duplicated the composition of the Earth’s atmosphere 3 or 4 billion years ago.
They added water (oceans), and electricity
(lightning) and made it a closed system.
The result…. Organic chemical reactions

The earliest fossils that you can see in rocks are called stromatolites . They are colonies of photosynthetic prokaryotes called cyanobacteria .
450 MA stromatolites from
Newfoundland

Evolution
Important Definitions:
Evolution : the transgenerational variation that occurs when social or biological forms adapt to their environment.
Involution : When organisms do not seem to outwardly change, despite modifications in their environments

Time
1
Time
2
Species A
Species B
Both eat the same stuff, but…
Species A breeds faster
After a while, Species A dominates the niche and…
Time
3
Eventually, Species B is driven into extinction
An example of survival of the fittest but not really evolution… unless the advantage is something that can be passed to future generations

Austrian Monk Gregor Mendel (1822-1884) experimented with peas in his garden and through his work, he made
2 important observations about evolutionary changes
(these are now considered biological principles):
1) Principle of segregation which states that genetically inherited features are passed on as separate, discrete units.
They do not blend together. Today we call these units genes .
2) Principle of independent assortment which states that genetic traits are inherited independently. Chance and chance alone determines which combinations of genes will be transmitted from parent to offspring.

Evolutionary change can proceed via one of two pathways…
1) In a series of relatively sudden distinct steps (
Punctuated Equilibria
)
Or
2) In a more or less continuous sequence (
Gradualism
).
Gradualism
Punctuated Equilibria
Common Ancestor
Common Ancestor

1) The Hadean (4.6 to 4.1 GA)
2) The Archean (4.1 to 2.5 GA)
Time Frame
Tectonics and Paleogeography
Life forms
(Web notes 16)

The Hadean and Archean Eons
Eon
Phanerozoic
Proterozoic
Archean
Hadean
Time
550 MA to 0 MA
2.5 GA to 550 MA
4.1 GA to 2.5 GA
4.6 GA to 4.1 GA

The Hadean Eon
Eon
Phanerozoic
Proterozoic
Archean
Hadean
Time
550 MA to 0 MA
2.5 GA to 550 MA
4.1 GA to 2.5 GA
4.6 GA to 4.1 GA

The Hadean Eon
(time chart anyone?)
1) Formation of the Earth (4.6 GA)
2) Formation of the Moon (4.4 GA?)
3) Late Heavy Bombardment (4.1- 3.8 GA)

The Hadean Eon
(time chart anyone?)
1) Formation of the Earth (4.6 GA)
2) Formation of the Moon (4.4 GA?)
3) Late Heavy Bombardment (4.1- 3.8 GA)
The Problem: the oldest rocks on the Earth are only 4.1 GA

The Hadean Eon
Or are they? new article Feb 24, 2014
Oldest dated minerals (zircons) found to date on the Earth are 4.4 billion years old. Indicate continental rocks existed on Earth right after the formation of the moon

The Hadean Eon
Eon
Phanerozoic
Proterozoic
Archean
Hadean
Time
550 MA to 0 MA
2.5 GA to 550 MA
4.4 GA? to 2.5 GA
4.6 GA to 4.4 GA?
Possible change is coming

The Archean Eon
Eon
Phanerozoic
Proterozoic
Archean
Hadean
Time
550 MA to 0 MA
2.5 GA to 550 MA
4.1 GA to 2.5 GA
4.6 GA to 4.1 GA

The Archean Eon
• The first usage of the term
Archean is credited to Sir
William Logan, a geologist with the GSC (Geological
Survey of Canada)

The Archean Eon
• The first usage of the term
Archean is credited to Sir
William Logan, a geologist with the GSC (Geological
Survey of Canada)
• He was studying very old rocks in northern/central
Canada

The Archean Eon
• The first usage of the term
Archean is credited to Sir
William Logan, a geologist with the GSC (Geological
Survey of Canada)
• He was studying very old rocks in northern/central
Canada
• “ PreCambrian ” granites and metamorphic rocks (no fossils), called the Canadian
Shield

The Canadian Shield http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
• No radiometric dating was possible in
Logan’s day, but he still managed to separate the
PreCambrian rocks into 2 primary components

The Canadian Shield
• Shield : very old
(>2.5 GA) igneous and metamorphic
“basement” rocks
(Granulites) http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif

The Canadian Shield http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
• Shield: very old
(>2.5 GA) igneous and metamorphic
“basement” rocks
(Granulites)
• Platform : younger
(550 MA-2.5 GA) sedimentary rocks

The Canadian Shield
• Together they represent continental cratons (e.g., the cores of continents) http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif

Shield Rocks
• Found around the world, but very rare in the USA

Shield Rocks
• Found around the world, but very rare in the USA http://www.fossilmuseum.net/Tree_of_Life/images/precambrian.jpg

Shield Rocks
• Very unfortunate….
Archean-aged rocks are rich in mineral resources
• Au, Ni, Fe, U, Pt, Co, Ti, diamonds, REEs

Canadian Shield
• Logan and others in the
GSC eventually subdivided the Canadian
Shield into different
(Tectonic) Provinces

Canadian Shield
• Logan and others in the
GSC eventually subdivided the Canadian
Shield into different
(Tectonic) Provinces

Canadian Shield
• Logan and others in the
GSC eventually subdivided the Canadian
Shield into different
(Tectonic) Provinces
• Superior is the biggest

Canadian Shield
• Logan and others in the
GSC eventually subdivided the Canadian
Shield into different
(Tectonic) Provinces
• Superior is the biggest
• Grenville is the youngest

Canadian Shield
• Today, with the aid of geophysics, we have resolved the extent of the provinces beneath younger cover rocks

Archean Tectonics
• We have lots of Archean rocks, but none from the Hadean.

Archean Tectonics
• We have lots of Archean rocks, but none from the Hadean.
• Still, we believe that the Earth’s crust and mantle started to
“differentiate” sometime during the Hadean.
“Light” rock rises http://www.le.ac.uk/geology/art/gl209/lecture7/image98.gif

Archean Tectonics
• We have lots of Archean rocks, but none from the Hadean.
• Still, we believe that the Earth’s crust and mantle started to
“differentiate” sometime during the Hadean.
• Two rock types:
•Komatiite (“heavy”, very fluid magma/lava rich in Mg and Fe)
•Tonalite (“light”, very viscous magma richer in Si, K and Na)

Archean Tectonics
Early continental crust = Tonalite (today it’s granite)
Early oceanic crust = Komatiite (today it’s basalt)

Archean Tectonics
Early continental crust = Tonalite (today it’s granite)
Early oceanic crust = Komatiite (today it’s basalt)
And the continents have been growing by accretion ever since

Archean Tectonics: Greenstone Belts
• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts
• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts
• One of the most interesting tectonic components in shield areas of the world are greenstone belts
• These rocks are a weird combination of igneous and deep water sedimentary rocks

Archean Tectonics: Greenstone Belts
• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts
• One of the most interesting tectonic components in shield areas of the world are greenstone belts
• They might be due to back arc spreading, crustal stretching or through a process that no longer operates today http://www.winona.edu/geology/MRW/mrwimages/beltfmtn.jpg

1.
Time Chart 1
2.
get ready for Spring Break (see 3 below)
3. study 20 hours a day each day next week (no beer)
1.
Origin of the Atmosphere and Hydrosphere
2.
Time Chart 1 ( due Thursday)
3.
Quiz: Fill in the blank diagram
More →

2.5 GA
4.1 GA
Geological Time Chart Assignment
Life Tectonics Paleogeography cyanobacteria
First prokaryotes greenstone belts
Big burp?
Tonalite continents?
Other
stuff
O
2
in oceans oldest rocks
Heavy Bombardment moon forms
Earth forms
4.6 GA

dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.