post 11

Totally 2 responses and 2 posts

Please first read the 3 pdf document to write 2 posts and answer my peers’ posts.

Complete the following 3 parts:(Totally 2 response and 2 posts)

This discussion assignment is for:

“A participation grade will be awarded based on your participation in the course discussion forum. To gain the full 5%, I expect you to contribute a minimum of two posts (as new threads) and eight replies (on different threads) throughout the course. E.g., you might share, or respond to, interesting content/links relevant to the course, start a discussion of a recent topic of course content, or pose a question about a topic. The content itself will not be graded, but must be a meaningful and valid contribution. As with all your conduct in this course, please keep the tone respectful.”

Example Post:

Topic: Coelacanth

By Krysta Bagnall

Found this short video which relates to the importance of fossils. The video is about coelacanth fish, which were thought to be extinct until the 1930’s! 

1. Please write a response to Krysta Bagnall about 70 words

Response example to Krysta Bagnall:

The subject of the Coelacanth is an interesting one. It serves as an excellent reminder that despite how much we have learned about our oceans over the last 500 years, there is still so much of it that remains unexplored.  

2. Please write a response to Algebra Young about 70 words

Topic: Sponge Love

By Algebra Young

Once again my deranged and fanatical love of sponges has an excuse to pop up! The worlds oldest confirmed multicellular animal fossil is a sponge that is dated to over 600 million years old. Its worth noting that the scientific community is often divided on sponges, some saying that they do, and others that they do not count as multicellular animals, so if you google the topic you will also find the second oldest multicellular animal fossil at 558 million years come up, Dickinsonia!

https://phys.org/news/2015-03-oldest-sponge-china.html

Example Response Algebra Young:

It is interesting to think how an organism that is so tiny can have such a substantial impact on Earth’s history. The article said that researchers from France, China, and The United States found the geologic formation which means that it took the efforts of three different countries to find a singular formation. It blows my mind how the sponge is over 600 million years old and mankind did not discover the sponge until semi-recently.

3. Write your own two topics about 100 words each

Instructions:

You might share, or respond to, interesting content/links relevant to the course, start a discussion of a recent topic of course content, or pose a question about a topic.

What is the correct sequence of events?

Fault A, Fault B,
then Dike A, Dike B

Dike B, then Dike A,
Fault A, Fault B

Fault B, then Dike B,
Fault A, Dike A

Fault A, Fault B,
then Dike B, Dike A

Stratigraphy and Geologic Time

Why is it important to document Earth history?
How do we know that one rock is older than another

(relative age)?
 Principles..
 Fossil record..

 How do we know the age of the Earth, and how has our
understanding changed over time?

 How can we use radioactivity to determine the (absolute)
age of a rock?

 How was the Geologic Timescale put together?

[Text: 8.1-8.6]

How old is the Earth?

Age #1: 6000 yrs + 6 days
(early biblical view, catastrophism: Ussher, 1600s)

Age #2: very old
(uniformitarianism, Hutton, late 1700s)

[last class]

Understand modern processes and their products

 apply this to rocks/features that likely formed the same
way in the past

e.g. how would you interpret:

– Ancient pillow basalts?
– Fine versus coarse-grained sedimentary layers?
– Offsets in layers?

Using uniformitarianism to read rocks

How old is the Earth?

Lord Kelvin (1890s):
(famous for Kelvin temp scale)

Used Earth’s temperature & thermal gradient,
assuming cooling from fully molten state

 Earth age #3: ~20 million years
BUT: radioactive sources not yet discovered

(Kelvin also predicted radios would not catch on,
flying airplanes not possible)

Image & further info:
http://apps.usd.edu/esci/creation/age/
content/failed_scientific_clocks/kelvin
_cooling.html

http://apps.usd.edu/esci/creation/age/content/failed_scientific_clocks/kelvin_cooling.html

How old is the Earth?

Edmund Halley (1700s):

Rivers bring dissolved salts to oceans
 Oceans should get more salty

How much time for initial freshwater
ocean to achieve current salinity?

 Calculated by John Joly (1899)

Image:
https://edukalife.blogspot.ca/201
5/07/biography-edmund-halley-
english.html

Image:
http://www.research.ie/feature
d-title/john-joly-defending-tcd-
against-1916-rebels

Halley/Joly Age of Earth Based on Salinity

 Earth age #4: ~80-150 million years
BUT did not account for salt recycling  Earth must be older

Salttoday=Saltoriginal + [(Saltadded/year)*(x years)]
Solve for x = age of Earth in years

Original:

Add:

Radioactive Decay

Radioactivity

discovered by Becquerel (1896):

– Many atoms decay spontaneously
– Decay produces energy (heat) & stable

daughter products

Solved 2 problems:
(1) An ongoing source of heat for Earth
(2) Absolute dating of igneous rocks

 Patterson (1953): first accurate age of the
Earth (Canyon Diablo meteorite)

 Earth age #5: 4.55 billion yrs

http://www.nobelprize.org/nobel_prizes/ph
ysics/laureates/1903/becquerel-bio.html

Ernest Rutherford developed radioactive dating
http://mp.natlib.govt.nz/detail/?id=7208&l=en

Isotopes
Isotopes of an element: same number of protons (Z: atomic #)

BUT different number of neutrons (N)

e.g. carbon isotopes: 12C, 13C, 14C

At.#,
isotope (mass)

#
protons

#
neutrons

6, 12C
stable

6 6

6, 13C
stable

6 7

6, 14C
radioactive

6 8
ZX , ,
A

6C
12

6C
13

6C
14

A (atomic mass) = Z + N
= protons + neutrons

Radioactivity

 Decay of unstable parent isotope to a stable daughter –
many steps

 Each isotope decays at its own fixed rate
– measured in half lives
(half life = time for ½ of parent atoms to decay/remain)

What is a radioactive half life?
 Half the original atoms decay during one half life
 Decay rates are exponential
 Heat produced by decay decreases exponentially

Earle, S. (2016): Online text Fig. 8.14

Linear vs
exponential?

e.g., decay of Uranium-238 (92 protons) to Thorium-234 (90 protons)

Radioactive Decay

Image: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

238U

234Th

Image: http://www.kgs.ku.edu/Extension/geotopics/earth_age.html

measure ratio of parent : daughter isotopes  # half lives
# half lives x half-life length  Age

Source: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

Which radiogenic isotope system to use for age of:

Meteorites?
~Billion-yr old rocks?
Glacial landforms?
Groundwater (H2O)?

Image: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

40K

40Ar

E.g., 40K  40Ar:
measure ratio of 40K (parent amount remaining)

to the total 40K + 40Ar (original parent amount)

Earle, S. (2016): Online text Ex. 8.3; Fig. 8.15

0.5 after 1.25 billion years
(one half life)

Example 1: U-Pb in zircons
Zircon: a resistant, Uranium-rich mineral
Ratios of Uranium, Thorium and Lead isotopes  age of mineral

Image: http://imetcal2.une.edu.au/web-content/Media.html

Animation on U-
Pb dating of

zircon minerals

http://www-personal.une.edu.au/%7Eimetcal2/Media.html

Earth’s oldest minerals
Jack Hills, Australia
4.4 billion years old

Wilde et al. (2001):
http://www.geology.wisc.edu/~valley/zi
rcons/Wilde2001Nature

Photo by Michael John Cheadle:
https://www.nsf.gov/news/news_images.jsp?cnt
n_id=104546&org=NSF

Image: Wikimedia Commons

[see next topic:
Early Earth]

Image: NASA (public domain)

Example 2: U-Pb system  Age of the Earth

Daughter isotopes of lead (Pb) in meteorites

Image by Geoffrey Notkin: Creative Commons

Canyon Diablo iron meteorite

Image: Dalrymple, G.B. (1986): Radiometric dating, Geologic Time, and the Age of the Earth: A reply to
“scientific” creationism, U.S. G.S. Open-File Report 86-110, 76 p.
https://pubs.usgs.gov/of/1986/0110/report

Image:
http://www.meteorlab.com/METEO
RLAB2001dev/murchy.htm

https://pubs.usgs.gov/of/1986/0110/report

Example 3: Evolution of Homo

Image: http://www.dailytelegraph.com.au/church-apologises-to-charles-darwin-over-theory-of-evolution/story-e6frewsr-1111117484124

Image: http://www.funbodytherapy.com/sample-page/gallery/evolution-of-man-to-computer/

Image:
http://donsnotes.com/science/bi
ology/evolution.html

Olduvai Gorge, Tanzania

Important fossil site of early
Homo species & stone tools

Image:
http://cw.routledge.com/text
books/9780415448789/colou

rimages.asp

Image: Encyclopaedia Britannica 2009

http://safariporini.com/olduvai-gorge.htm

“Lucy’s” Footprints
(in volcanic ash)

K/Ar dating of volcanic ash 1 m below fossil  3.2 million yrs

Image: http://www.ancientdigger.com/2011/07/laetoli-footprints-explained.html

http://www.dailymail.co.uk/sciencetech/article-
3099430/Mysterious-fossils-reveal-new-species-
early-HUMAN-jawed-hominid-lived-alongside-Lucy-
3-4-million-years-ago.html

our earliest known direct ancestor

LUCY

Putting dates on humankind’s evolution

Image: http://www.talkorigins.org/faqs/homs/species.html

Brain size of Homo

EOS120 class

Image: https://ncse.com/book/export/html/1764 (Graphic by Nick Matzke)

https://ncse.com/book/export/html/1764

Example 4: 14C dating – young events
(a few hundred to ~40,000 yrs)

 14C produced in upper
atmosphere by cosmic ray
bombardment of 14N

 14C incorporated in CO2 
absorbed by living matter

 14C continually replaced in
living organisms, but after
death the 14C decays to 14N

 Ratio of 14C to 12C  age
of the matter once it
stopped replacing 14C

Image: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

Caveat – ‘Bomb’ Carbon-14
nuclear weapons testing
 simulated atmospheric production of C-14 in unnatural quantities

Image: http://www.thefullwiki.org/Partial_Test_Ban_Treaty

Read more at:
https://www.radiocarbo
n.com/carbon-dating-
bomb-carbon.htm

https://www.radiocarbon.com/carbon-dating-bomb-carbon.htm

https://www.radiocarbon.com/carbon-dating-bomb-carbon.htm

Image: Kalish, J.M. (1993), Earth and Planetary Science Letters v. 114 (4): 549-554.

Earle, S. (2019): Online text Fig. 8.4.5

A Geologic Time Scale

how to correlate across vast sections of space and
time?

Where to start?

Aristotle, da Vinci: fossils as ‘ancient’ life

Steno: 17th century – “Superposition”

Smith, Lyell: 1800s, ID of strata using fossils – correlation

1896 – Radioactivity discovered  absolute ages

Arthur Holmes: 1913 – first time scale

1977: Official Modern Scale

Earth’s timescale: 4.55 billion yrs – a big number

Counted at 3 numbers per second:

 1 million in ~4 days

 over 10.5 years to count to one billion

 4.6 billion would require 50 years of non-stop counting

The Geologic Time Scale
– Based on rock sequences in Europe correlated
worldwide; includes use of fossils, radiometric dates

– Period divisions mark changes or loss in fauna

www.washingtonpost.com

http://r.search.yahoo.com/_ylt=A86.JyjOIfJWpW0A5QYnnIlQ;_ylu=X3oDMTE0c3AzaWpzBGNvbG8DZ3ExBHBvcwMxBHZ0aWQDUFJEQ1RMMV8xBHNlYwNzYw–/RV=2/RE=1458737742/RO=10/RU=http:/www.washingtonpost.com/blogs/wonkblog/wp/2014/02/11/there-have-been-five-mass-extinctions-in-earths-history-now-were-facing-a-sixth/RK=0/RS=i0gtGjKjGYAp7h4yr_SLjQIzGSs-

Faunal successions (coming and going of organisms) divide up periods
of time
Many divided by extinction (species loss), others by species emergence

Image: Edwards, L.E. & Pojeta, J. Jr. (1994): Fossils, rocks and time, U.S. Gov. Printing Office 1998-675-105, 24p.

Eons  Eras  Periods

Hadean
4000

541

2.6

Download latest geological time scale here (March 2020)

485
444
419

252
201
145

4550

Carboniferous
299

359

https://stratigraphy.org/ICSchart/ChronostratChart2020-03

Stratigraphy and Geologic Time

 Deposition and the rock record
 Biology (fossils) in the rock record
 Relative vs. absolute time
 Relative ages from principles (e.g., X-cutting relations)
 Dating (ages) using radioactivity in minerals and

organic matter
 Time – is of immense magnitude
 Precise chronology of the ‘tempo’ of earth events and

evolution
 Applied in geology and archeology

• Slide Number 1

Stratigraphy and Geologic Time

• Slide Number 3
• Slide Number 4
• Slide Number 5
• Slide Number 6
• Slide Number 7
• Slide Number 8
• Slide Number 9

Radioactivity

• Slide Number 11
• Slide Number 12
• measure ratio of parent : daughter isotopes  # half lives �# half lives x half-life length  Age
• Slide Number 14

Which radiogenic isotope system to use for age of:

• Slide Number 16
• Slide Number 17
• Slide Number 18
• Slide Number 19
• Slide Number 20
• Slide Number 21

Example 3: Evolution of Homo

• Slide Number 23
• Slide Number 24

Olduvai Gorge, Tanzania

• “Lucy’s” Footprints �(in volcanic ash)
• Slide Number 27

Brain size of Homo

• Slide Number 29
• Slide Number 30
• Slide Number 31
• Slide Number 32
• A Geologic Time Scale��how to correlate across vast sections of space and time?

Where to start?
Earth’s timescale: 4.55 billion yrs – a big number

• Slide Number 36
• Slide Number 37
• Slide Number 38

Eons  Eras  Periods

• Slide Number 40

Stratigraphy and Geologic Time

Course announcements

Remaining content: [all course lecture recordings will be posted]
 4 lectures: 4.6 billion years of Earth history
 2 lectures: Resources & human impact
 No class on Fri Dec 4

all UVic classes cancelled 11:30-12:30 to mark National Day of
Remembrance and Action on Violence against Women

 Review session Mon Dec 7, time TBD (recording will be posted)

Remaining assessment:
 Q9: 9 pm Nov 23; Q10: 9 pm Dec 7; Q11, Q12: 1 pm Dec 9
 Quizzes: lowest score dropped – make the last few count!
 Discussion contributions: 1 pm Dec 9
 Final exam: 2 pm Wed Dec 9

Course Experience Survey – your feedback is VALUED!

Stratigraphy and Geologic Time

Why is it important to document Earth history?
How do we know that one rock is older than another

(relative age)?
Principles..
Fossil record..

How do we know the age of the Earth, and how has our
understanding changed over time?

How can we use radioactivity to determine the (absolute)
age of a rock?

 How was the Geologic Timescale put together?

[Text: 8.1-8.6]

The Geologic Time Scale
– Based on rock sequences in Europe correlated worldwide; includes
use of fossils, radiometric dates

– Period divisions mark changes or loss in fauna

www.washingtonpost.com

http://r.search.yahoo.com/_ylt=A86.JyjOIfJWpW0A5QYnnIlQ;_ylu=X3oDMTE0c3AzaWpzBGNvbG8DZ3ExBHBvcwMxBHZ0aWQDUFJEQ1RMMV8xBHNlYwNzYw–/RV=2/RE=1458737742/RO=10/RU=http:/www.washingtonpost.com/blogs/wonkblog/wp/2014/02/11/there-have-been-five-mass-extinctions-in-earths-history-now-were-facing-a-sixth/RK=0/RS=i0gtGjKjGYAp7h4yr_SLjQIzGSs-

Faunal successions (coming and going of organisms) divide up periods
of time
Many divided by extinction (species loss), others by species emergence

Image: Edwards, L.E. & Pojeta, J. Jr. (1994): Fossils, rocks and time, U.S. Gov. Printing Office 1998-675-105, 24p.

Eons  Eras  Periods

Hadean

4000

541

2.6

Download latest geological time scale here (March 2020)

485
444
419
459
323
299
252
201
145

4550

https://stratigraphy.org/ICSchart/ChronostratChart2020-03

Earle, S. (2019): Online text Fig. 8.1.2 & 8.1.3

Stratigraphy and Geologic Time

 Deposition and the rock record
 Biology (fossils) in the rock record
 Relative vs. absolute time
 Relative ages from principles (e.g., X-cutting relations)
 Dating (ages) using radioactivity in minerals and

organic matter
 Time – is of immense magnitude
 Precise chronology of the ‘tempo’ of earth events and

evolution
 Applied in geology and archeology

The Precambrian

Image: http://www.physci.mc.maricopa.edu/d43/glg/Study_Aids/geotime/time_l_fx1

541
4000Ma

4600 Ma

How old are Earth’s oldest known minerals,
dated using U-Pb isotopes?

Cambrian

Proterozoic

Archean

Hadean
Image: http://www.physci.mc.maricopa.edu/d43/glg/Study_Aids/geotime/time_l_fx1
541
4000Ma
4600 Ma

Early Earth: The First 2 Billion Years



Where are Precambrian rocks found today?

 What were conditions like on early Earth?

 How did the Moon form?

 Evidence for liquid water?

 Evidence for continents?

 The origin of life on Earth?

[Text: 8.1, 22.4]

Earle, S. (2016): Online text Fig. 8.3

P R E C A M B R I A N

40
00

M
a

54
1

M
a

How do we know about Earth in the
Precambrian?

 Precambrian rocks are poorly exposed

 eroded or metamorphosed or deeply buried beneath
younger rocks

 Fossils are seldom found in Precambrian rocks

 Long time ago – Does “Uniformitarianism” apply?

 87% of Earth history is poorly known – a fragmented record

Earle, S. (2016): Online text Fig. 8.3
P R E C A M B R I A N

First 2 billion years
Hadean: 4.6-4.0 Ga: no rocks preserved
Archean: 4.0-2.5 Ga

40
00

M
a

54
1
M
a

Great Precambrian Events

Image: http://geo.msu.edu/extra/geogmich/Precambrian.html~4600

4000

2500

1600

1000
541 Ma

4.55 to 4.0 Ga – The “Hadean” (Hades: hell like – but was it?)

http://novacelestia.com/space_art_solar_system/earth.html

First 50 Myr – Earth’s core/layering

 Layering requires process of differentiation

 Initial heating, partial melting:
‘magma ocean’

 Fe metal sinks to form core

 Less dense ‘silicate’ melt (Si,O, remaining other
elements) forms lighter mantle & crust

Recall: Why was early Earth hot?
 Heat from gravitational contraction
 Accretionary heat from asteroid impacts
 Radioactive decay

Image: http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter08-05.html

Collisions with asteroids and planetismals

http://novacelestia.com/space_art_solar_system/earth.html

Radiogenic Heat Production (K, U, Th)

Origin of the Moon?
~4.5 Ga

Image: NASA

Giant Impact Hypothesis (the Big Splash)

(Theia)

Image by Joe Tucciarone: https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question38.html

Earth’s oldest minerals
Jack Hills, Australia
4.4 billion yr-old zircons

Wilde et al. (2001):
http://www.geology.wisc.edu/~valley/zi
rcons/Wilde2001Nature

Photo by Michael John Cheadle:
https://www.nsf.gov/news/news_images.jsp?cnt
n_id=104546&org=NSF

Image: Wikimedia Commons

Isotope data
 Magma in which the zircons

formed included melt from
crustal material that must have
interacted with liquid water

 Liquid water present during early
Hadean

http://www.geology.wisc.edu/%7Evalley/zircons/Wilde2001Nature

Hadean: Earth’s oldest minerals
Archean: Earth’s oldest rocks (oldest preserved)

P R E C A M B R I A N

Archean
(4.0 to 2.5 Ga)

40
00
M
a
54
1
M
a
Earle, S. (2016): Online text Fig. 8.3

Where are Precambrian rocks found today?

Green > 2.5 Ga
Red > 1.8 Ga,
Orange > 1.0 Ga
Ga = giga years

Archean rocks: form cores of continents – cratons
– metamorphosed granite, volcanic & sedimentary rocks in ‘belts’

Image modified from http://earthsci.org/mineral/mindep/diamond/Whlook.html

Exposure of Archean crust in North America: the Canadian shield

Earth’s Oldest Rocks

Acasta

Image modified from http://news.bbc.co.uk/2/hi/science/nature/2546019.stm

Acasta Gneiss,
NWT
3.962 Ga

Oldest rock age
(igneous origin)

Images:
http://www.geo.titech.ac.jp/lab
/ueno/research.html

Porpoise Cove, Quebec 3.8 Ga
Metamorphic rocks (parent:
either volcanic or sedimentary
rocks that formed near surface)

https://en.wikipedia.org/wiki/Nuvvuagittuq_Greenstone_Belt

Isua, West Greenland
3.8 Ga

Deformed pillow lavas

Implication?

 subaqueous eruption
 ‘ocean water’ existed

Image: http://www.mue.titech.ac.jp/rock/isua/title02/

modern
Archean

Sub-aqueous eruptions

Image:
http://www.punaridge.org/doc/factoids/eruptions
/default.htm

Image:
http://umanitoba.ca/science/geological_sciences/faculty/arc/pictures/pillows

Earth’s oldest soil
Pilbara paleosol (fossil soil) – 3.46 Ga

Implication?

Problem – Early Earth Surface Temperature Should be
Freezing (no liquid water)

4.5 Ga:
Sun’s output only 70%
that of today
(Stellar evolution)

Too cold to maintain a
liquid ocean
 refuted by geologic
evidence

(Sagan and Mullen, 1972)

How to explain?

‘Faint Young Sun’ paradox

Image: http://www.everythingselectric.com/faint-young-sun-paradox/

Why so few rocks older than ~3.8 Ga?
Late Heavy Bombardment

 ‘Impact zones’ & impact melt rocks on the Moon
 Ages peak at 3.8 Ga
 Consequence for Earth’s surface nearby?  obliterated

Image: http://www.origin-life.gr.jp/3603/3603055/fig2

Why is there such a record on Moon, but not on Earth?

Image: http://seprin.info/2016/11/18/asteroid-strike-made-instant-himalayas/

Archean Plate Tectonics?

 Higher internal temperature of the Earth

 Faster plate motion?

 Many small, mobile plates

 Early crust oceanic – continents formed later

Evidence for continents in the Archean (4-2.5 Ga)?

 Oldest rocks (Acasta Gneiss, 3.96 Ga; Isua pillow lavas, 3.8 Ga)
 3.46 Ga fossil soil (paleosol): Pilbara region, Australia

Liquid oceans  warm greenhouse atmosphere

Subaerial weathering, soil formation

Continents above sea level

Early Atmosphere

 Initial H, He lost to space
 Volcanic outgassing  water vapour, CO2, SO2, H2S, CH4..
 Meteorites/comets  water, nitrogen

 Convection in core  magnetic field deflects solar wind, so
gases/atmosphere can accumulate

 Early atmosphere dense, very hot
 Mostly water vapour, CO2, nitrogen

 Very little oxygen  Earth inhospitable to most forms of
life as we know it today

Archean Fossils

Most Archean fossils: stromatolites and single cells
Stromatolite:
dome-like layered structure formed from mat-like colonies (of single-
celled cyanobacteria) that trap sediment and calcium carbonate

Oldest stromatolites: 3.5 Ga (W. Australia)

Image: http://hoopermuseum.earthsci.carleton.ca/stromatolites/ARCHEAN1.htm

https://www.newscientist.com/article/2217747-fossilised-microbes-from-3-5-billion-years-ago-are-oldest-yet-found/

https://www.newscientist.com/article/2217747-fossilised-microbes-from-3-5-billion-years-ago-are-oldest-yet-found/

Modern stromatolites

(extreme environments:
e.g., high-salinity Shark Bay, Australia)

Image:
http://geol.queensu.ca/museum/index.ph
p?option=com_content&view=article&id=
50&Itemid=57

Archean single-celled micro-organisms

 Simplest form of modern carbon-based life
 Lack DNA-packaging nuclei
 Only life on Earth for next 2 billion years

Infer:
Photosynthesis: occurring by 3.0 Ga,

possibly as early as 3.5 Ga
 oxygen

Image:
http://hoopermuseum.earthsci.carleton.ca/stromatolites/ARCHEAN1.htm

Origins of Life: What is Needed?

 Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur

 Proteins (chains of amino acids): build living materials,
catalysts for reactions in organisms

 Nucleic acids (DNA, RNA)

 Organic phosphorus: transforms light/chemical fuel  energy

 Cell membrane: encloses cell components

Amino acids formed in simulated early Earth atmosphere

Miller and Urey experiment
(1950’s):

Formed amino acids (building
blocks of life) from:

H2, CH4 (methane), NH3
(ammonia), H2O (steam) gases
& sparks (simulated lightning)

Image: http://history.nasa.gov/SP-349/ch1.htm

Early Organisms

 Developed in presence of an oxygen-free atmosphere
(anaerobic – no oxygen for respiration)

 No oxygen  no ozone shield (O3) against harmful
ultraviolet radiation

Where to live?
 Below sediment – e.g., stromatolites
 Beneath the surface of rocks?
 Under water?

Deep-sea hydrothermal vents

 Hyperthermophiles or

microbes thrive in seawater
hotter than 100oC

 Derive energy by
chemosynthesis, not by
photosynthesis

 Hyperthermophiles are
Archaea, different from
bacteria (also single-celled)

 Possible environment for
origin of life

(or did life arrive on an asteroid?)

Shen and Buick, 2004

O2 –rich atmosphere
led to complex life forms?

The genetic tree of life

Single-celled
Single-celled
Different genes

Multi-celled,
complex

Summary: Hadean-Archean – long book with few pages

 Age of Solar System 4.567 Ga
 Oldest detrital zircons ~ 4.4 Ga Western Australia: implication of oceans
 Oldest rocks 3.96 Ga, Acasta Gneisses, NWT Canada
 Oldest supracrustal volcanics and seds 3.8 Ga, Isua, Greenland
 Oldest well preserved fossils 3.5 Ga, W. Australia

Image:
http://elements.geosci
enceworld.org/conten
t/gselements/2/4/201
/F3.large

Archean… Thoughts

 Faint Young Sun…
 More radiogenic

heat production
 No or little ozone
 Only simple life
 Fragmented record

 Earth’s surface T
 Plate tectonics?
 Life challenges
 Crust?

Course announcements
Stratigraphy and Geologic Time
• Slide Number 3
• Slide Number 4
• Slide Number 5

Eons  Eras  Periods

• Slide Number 7
• Slide Number 8

Stratigraphy and Geologic Time

• Slide Number 10
• Slide Number 11

Early Earth: The First 2 Billion Years

• Slide Number 13
• How do we know about Earth in the Precambrian?
• Slide Number 15
• Slide Number 16
• Slide Number 17

First 50 Myr – Earth’s core/layering

• Slide Number 19
• Slide Number 20
• Slide Number 21
• Slide Number 22
• Slide Number 23
• Slide Number 24
• Slide Number 25
• Slide Number 26
• Slide Number 27
• Slide Number 28
• Slide Number 29
• Slide Number 30
• Slide Number 31
• Slide Number 32
• Slide Number 33
• Problem – Early Earth Surface Temperature Should be Freezing (no liquid water)��
• Why so few rocks older than ~3.8 Ga?�Late Heavy Bombardment
• Slide Number 36
• Archean Plate Tectonics?�
• Evidence for continents in the Archean (4-2.5 Ga)?�
• Early Atmosphere�

Archean Fossils

• Slide Number 41

Archean single-celled micro-organisms
Origins of Life: What is Needed?

• Amino acids formed in simulated early Earth atmosphere�
• Early Organisms�

Deep-sea hydrothermal vents

• Slide Number 47

Summary: Hadean-Archean – long book with few pages
Archean… Thoughts

Earth’s Internal Structure

What layers make up the Earth?
How does composition change with depth?

How do physical properties change?

 How do we know?
 Crustal structure?

 Deeper structure: e.g., that the outer core is liquid?

[Text: 9.1]

Earle, S. (2016): Online
text Fig. 9.6b

[last class]

How do we know that the outer core is liquid?

(1) S waves cannot travel through it
(2) P waves are slowed

Earle, S. (2016): Online text Fig. 9.6a

How do we know that the outer core is liquid?
(3) Slowed P waves must be refracted downward (not upward)

 shadow zone (where no P waves arrive)

diagram:
refraction at outer core

Earle, S. (2019): Online text Fig. 9.1.6

Other seismic discontinuities

In mantle:
410 km, and 660 km:
– phase changes to denser

mineral structures

Deep:
2900 km – core/mantle

boundary (CMB)
5150 km – inner core/outer

core boundary

Earle, S. (2016): Online text Fig. 9.6a

7

Aegean S. Kuril Izu-Bonin

Kearey et al. (2009): Global Tectonics, 3rd edn., Wiley-Blackwell, Plate 9.2

How do we know that the inner core is solid iron?

 Gravitational pull exerted by Earth
 requires high-density iron inner core

 The whole Earth oscillates after large earthquakes
 inner core must be solid

Earth’s Internal Structure – Summary

 3 main sections by composition: crust, mantle, and core

 Physical properties change with depth in response to
increased P and T

 5 main sections by physical properties: rigid lithosphere,
partially molten asthenosphere, rigid mesophere, liquid
outer core, solid inner core

 Boundaries in the Earth’s interior act as seismic
discontinuities – abrupt changes in the velocity of seismic
waves travelling through the Earth

Stratigraphy and

Geologic Time

 Why is it important to document Earth history?
 How do we know that one rock is older than another

(relative age)?
 Principles..
 Fossil record..

 How do we know the age of the Earth, and how has our
understanding changed over

time

?

 How can we use radioactivity to determine the (absolute)
age of a rock?

 How was the Geologic Timescale put together?

[Text: 8.1-8.6]

Why document Earth history?

 The past may be the key to the future:
changes occur in cycles, patterns repeat

 How has the Earth changed?
– e.g. CO2 levels, climate, sea level, landmasses,
biological evolution & extinctions, Wilson cycles

HOWEVER:
 Almost all of Earth’s history predates humans

How is Earth history documented?  The Rock Record

Sediments laid down in layers (strata)  a stratigraphy of events:
a record of earth processes over geological time

deep

shallow

deep
shallow

Image: http://explanet.info/Chapter02.htm

Reading the book (the stratigraphic record)
Main concepts:

1) Beds (strata, sedimentary units) – horizontal – bound by bedding
planes

2) Multiple beds make up a stratigraphic ‘sequence’ – bound by
erosional episodes due to fluctuations in sea-level, uplift

3) Strata contain fossilized flora and fauna
4) The rock record is incomplete at any one place (gaps in time)

L. Leonard

Biostratigraphy

Fossils
 Used in correlation of strata

 Occur over a stratigraphic range

 Organisms: also provide info on environment
– some organisms tolerate very wide environmental

conditions; others do not
E.g., different trilobite species:
bottom dwellers vs. floaters vs. swimmers

Image:
http://www.wilsonmuseum.org/treasures
/treasures_new2.html

Two ways to view geologic time:

(1) Relative time
– dating by sequence of events

– “older” vs. “younger”
– placed in order

(2) Absolute time
– numerical dating using radioactive

decay in minerals

Geologic Time

Image: http://www.evolution.berkeley.edu/evosite/lines/IIIAchronology.shtml

How to establish the order of geological events?

Relative age dating:
Principles
1) Superposition
2) Original horizontality
3) Faunal (& floral) succession
4) Inclusions
5) Cross-cutting relations

(1) Principle of Superposition:
In an undisturbed stratigraphic sequence, the rocks at the top

are youngest

Colorado River, Utah
Image: Lutgens, Tarbuck,
Tasa (2006): Essentials of
Geology, 9th edn., Pearson.

[17th century:
Nicolas Steno]

(2) Original Horizontality:
Sedimentary layers are deposited in horizontal units/beds

Inclined layering  layers were tilted from initial horizontal
orientation some time after

deposition

Images: Lutgens, Tarbuck, Tasa (2006):
Essentials of Geology, 9th edn., Pearson.

Possible Problem: overturned strata in mountain belts (deformation)

 need to know ‘which way is up’ in a sedimentary package

Image:
https://www.nps.gov/parkhistory/online_books/geology/publications/
pp/296/sec2a-2.htm

http://college.cengage.com/geology/resources/protected/physicallab/thelab/geolog
icmaps/activities/activity1/activity1.htm

Large gaps of time between deposition of layers (strata):
unconformities

“Hutton’s unconformity”, Siccar Point, Scotland

How does an angular unconformity form?

65 Myr
missing

deposition,

tilting,

erosion,

deposition

Image: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

time

Angular unconformity
Beds above: ~ horizontal
Beds below: dip down to right (~500 Myr history missing)

Earle, S. (2016): Online text Fig. 8.8

(3) Faunal (& Floral) Succession:
Sedimentary layers contain fossilized flora & fauna

Organisms succeed each other vertically in a specific, reliable
order  fossil record
 Rocks with similar fossils are (generally) of similar age

e.g., Neanderthal bone (young) never found in same strata as a
Tyrannosaurus Rex (much older)

Earle, S. (2016): Online text Fig. 8.10

66 Ma252 Ma541 Ma

Tarbuck, Lutgens, Tsujita (2015): Earth: Introduction to
Physical Geology, 4th Cdn. Edn., Pearson.

Which are useful index fossils?

(4) Inclusions
Older rocks “included” in younger rocks
– e.g., blocks eroded from country rock by intruding magma

Earle, S. (2016): Online text Fig. 8.6a

xenolith

Earle, S. (2016): Online text Fig. 8.6b

Sedimentary inclusion: “rip-up” clast

(5) Cross-cutting relations
Older rocks are “cross-cut” by younger rocks or features

(e.g., dykes, faults, erosion surfaces)

http://www.geosociety.org/Earthcache/Images/block%20diagram1182008

How many? Relative age?

Image: Hamblin & Christiansen (2003): Earth’s Dynamic Systems, 10th edn., Prentice Hall

What principles explain the sequence of events A to T?

http://www.wiringdiy.com/static/block-diagram-of-well-who-knows-where-just-try-to-put-things-in-1541910

Layers B to G are younger
than A:
principle of superposition
H younger than A-G:
_____________________
I younger than A-H:
_____________________
J,K,L younger than I:
_____________________
M younger than A-L:
_____________________
N,O younger than M:
_____________________
P,Q younger than A-O:
_____________________
R younger than A-Q:
_____________________
S,T younger than A-Q:
_____________________

How old is the Earth?

Archbishop James Ussher (1600’s):

early biblical view:
Earth age #1: 6 days + 6000 yrs

 so much in so little time!

Catastrophism: Earth history must be
shaped by sudden, violent processes
(e.g., biblical flood)

Image: Wikimedia Commons

Uniformitarianism
Sir James Hutton (late 1700’s):

Processes forming sediment layers today
are gradual

 Uniformitarianism:
“the present is the key to the past”

 Earth age #2: very old
(at least millions of years)

“no vestige of a beginning,
no prospect of an end”

– radical idea at the time
– same conclusion later reached by Lyell, Darwin

http://www.smithsonianmag.com/history/fa
ther-modern-geology-youve-never-heard-
180960203/?no-ist

• Slide Number 1

Earth’s Internal Structure

• Slide Number 3

How do we know that the outer core is liquid?
How do we know that the outer core is liquid?

• Other seismic discontinuities�
• Slide Number 7

How do we know that the inner core is solid iron?
Earth’s Internal Structure – Summary

• Stratigraphy and Geologic Time
• Slide Number 11
• Slide Number 12
• Reading the book (the stratigraphic record)�Main concepts:

Biostratigraphy
Geologic Time

• Slide Number 16
• Slide Number 17
• Slide Number 18
• Slide Number 19
• Slide Number 20
• Slide Number 21
• Slide Number 22
• Slide Number 23
• Slide Number 24
• Slide Number 25
• Slide Number 26
• Slide Number 27
• Slide Number 28
• Slide Number 29
• Slide Number 30
• Slide Number 31
• Slide Number 32
• Slide Number 33
• Slide Number 34
• Slide Number 35
• Slide Number 36
• Slide Number 37
• Radioactivity
• Slide Number 39
• Slide Number 40
• measure ratio of parent : daughter isotopes  # half lives �# half lives x half-life length  Age
• Slide Number 42
• Which radiogenic isotope system to use for age of:
• Slide Number 44
• Slide Number 45