UNIVERSITY OF SOUTH ALABAMA
GY 112: Earth History
Lecture 16:
The Hadean and Archean
Instructor: Dr. Douglas W. Haywick
Last Time
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)
Earth’s Early Atmosphere
Today:
N2= 78%; O2=21%; Ar=1%;
H2O=variable; CO2=0.03%
4.1 GA:
N2; HCl; SO2; CO2; CH4; NH3; NO2; H2O
NO…. O2
How do we know?
Earth’s Early Atmosphere
Volcanic eruptions
Earth’s Early Atmosphere
Venus
Earth’s Early Atmosphere
4.1 GA:
N2; HCl; SO2; CO2; CH4; NH3; NO2; H2O
Earth’s First Life Forms
The Western Australia beasties
were very “simple” single celled
organisms like today’s bacteria
= prokaryotes
The Earliest “Visible” Fossils
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
Stromatolites
How Did Life Get Started?
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
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
Time
3
Species A
Both eat the
same stuff,
Species B
but…
Species A breeds faster
After a while, Species A
dominates the niche and…
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
How does evolution work?
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.
How does evolution work?
Evolutionary change can proceed via one of two pathways…
1) In a series of relatively sudden distinct steps (Punctuated
Or
Equilibria)
2) In a more or less continuous sequence (Gradualism).
Gradualism
Punctuated Equilibria
Common Ancestor
Common Ancestor
Today’s Agenda
1)
2)
The Hadean (4.6 to 4.1 GA)
The Archean (4.1 to 2.5 GA)
Time Frame
Tectonics and Paleogeography
Life forms
(Web notes 16)
The Hadean and Archean Eons
Eon
Time
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.1 GA to 2.5 GA
Hadean
4.6 GA to 4.1 GA
The Hadean Eon
Eon
Time
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.1 GA to 2.5 GA
Hadean
4.6 GA to 4.1 GA
The Hadean Eon
Key events (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
Key events (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?
published 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
Time
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.4 GA? to 2.5 GA
Hadean
4.6 GA to 4.4 GA?
Possible change is coming
The Archean Eon
Eon
Time
Phanerozoic
550 MA to 0 MA
Proterozoic
2.5 GA to 550 MA
Archean
4.1 GA to 2.5 GA
Hadean
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
• No radiometric
dating was
possible in
Logan’s day, but
he still managed
to separate the
PreCambrian
rocks into 2
primary
components
http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
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
• Shield: very old
(>2.5 GA)
igneous and
metamorphic
“basement” rocks
(Granulites)
• Platform: younger
(550 MA-2.5 GA)
sedimentary rocks
http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
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
http://www.iml.rwth-aachen.de/projekte/Fig1hp.jpg
• Found around the
world, but very rare
in the USA
Shield Rocks
http://www.iml.rwth-aachen.de/projekte/Fig1hp.jpg
• Found around the
world, but very rare
in the USA
http://www.fossilmuseum.net/Tree_of_Life/images/precambrian.jpg
Shield Rocks
Source: Geological Survey of Canada
• 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
http://www.mndm.gov.on.ca
• One of the most interesting tectonic components in shield areas
of the world are greenstone belts
Archean Tectonics: Greenstone Belts
http://www.mndm.gov.on.ca
• 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
http://www.mndm.gov.on.ca
• 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
Today’s Homework
1. Time Chart 1 (next page)
2. study 20 hours a day each day next week (no beer)
Next Time
1. Origin of the Atmosphere and Hydrosphere
2. Time Chart 1 (due Thursday March 2)
3. Quiz: multiple choice
More →
Geological Time Chart Assignment
2.5 GA
Archean
Life
Tectonics
Paleogeography
Other
stuff
O2 in oceans
cyanobacteria
greenstone
belts
First
prokaryotes
Tonalite
continents?
4.1 GA
oldest rocks
Hadean
Heavy Bombardment
Big burp?
moon forms
4.6 GA
Earth forms
GY 112: Earth History
Lecture 16: Hadean and Archean
Instructor: Dr. Doug Haywick
[email protected]
This is a free open access lecture, but not for commercial purposes.
For personal use only.