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 Species A Both eat the Species B same stuff, but… Species A breeds faster Time 2 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
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 Equilibria) Or 2) In a more or less continuous sequence (Gradualism).
Gradualism Punctuated Equilibria
Common Ancestor Common Ancestor Today’s Agenda
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 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 Possible change is coming Hadean 4.6 GA to 4.4 GA? 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
• Found around the world, but very rare in the USA aachen.de/projekte/Fig1hp.jpg - http://www.iml.rwth Shield Rocks
• Found around the world, but very rare in the USA aachen.de/projekte/Fig1hp.jpg - http://www.iml.rwth
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 Source: Geological Survey Source: Geological Canada of Survey 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
http://www.mndm.gov.on.ca 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 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
http://www.mndm.gov.on.ca 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 Life Tectonics Paleogeography Other
stuff
O2 in oceans cyanobacteria greenstone belts
Archean
First Tonalite prokaryotes continents? 4.1 GA oldest rocks
Heavy Bombardment
Hadean Big burp? moon forms Earth forms 4.6 GA 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.