GY 112: Earth History

Lecture 16: The Hadean and Archean

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

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

(Web Lectures 14 & 15)

Evolution 2: How it works 1) Definition of Evolution

2) Darwin's law of natural selection (gradualism, punctuated equilibria) 3) examples of evolutionary development

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

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

= prokaryotes

Earth’s First Life Forms

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

An example of survival of the fittest but not really evolution… unless the advantage is something that can be passed to future generations

Time 1

Time 3

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…

Eventually, Species B is driven into extinction

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).

Punctuated Equilibria

Common Ancestor

Gradualism

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 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 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 Archean Eon

• 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

http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif

• Shield: very old (>2.5 GA) igneous and metamorphic “basement” rocks (Granulites)

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

http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif

• Together they represent continental cratons (e.g., the cores of continents)

The Canadian Shield

http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif

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

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

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http://www.fossilmuseum.net/Tree_of_Life/images/precambrian.jpg

• Very unfortunate…. Archean-aged rocks are rich in mineral resources

• Au, Ni, Fe, U, Pt, Co, Ti, diamonds, REEs

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• 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

Canadian Shield

• Superior is the biggest

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

Canadian Shield

• Superior is the biggest • Grenville is the youngest

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

Canadian Shield

• 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.

Archean Tectonics

http://www.le.ac.uk/geology/art/gl209/lecture7/image98.gif

“Light” rock rises

• 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

• 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.

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

• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts

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• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts

http

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• One of the most interesting tectonic components in shield areas of the world are greenstone belts

Archean Tectonics: Greenstone Belts

http

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• These rocks are a weird combination of igneous and deep water sedimentary rocks

• 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

http://www.winona.edu/geology/MRW/mrwimages/beltfmtn.jpg

• They might be due to back arc spreading, crustal stretching or through a process that no longer operates today

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 →

Life Tectonics Paleogeography Other stuff

Arc

hean

H

adea

n

moon forms Earth forms

First prokaryotes

cyanobacteria

oldest rocks

greenstone belts

Big burp?

Tonalite continents?

O2 in oceans

4.6 GA

4.1 GA

2.5 GA

Heavy Bombardment

Geological Time Chart Assignment

GY 112: Earth History

Lecture 16: Hadean and Archean

Instructor: Dr. Doug Haywick dhaywick@southalabama.edu

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