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
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
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
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
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
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
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?
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
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.
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
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 11
- Slide Number 12
- measure ratio of parent : daughter isotopes # half lives �# half lives x half-life length Age
- Slide Number 14
- Slide Number 16
- Slide Number 17
- Slide Number 18
- Slide Number 19
- Slide Number 20
- Slide Number 21
- Slide Number 23
- Slide Number 24
- “Lucy’s” Footprints �(in volcanic ash)
- Slide Number 27
- 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?
- Slide Number 36
- Slide Number 37
- Slide Number 38
- Slide Number 40
Stratigraphy and Geologic Time
Radioactivity
Which radiogenic isotope system to use for age of:
Example 3: Evolution of Homo
Olduvai Gorge, Tanzania
Brain size of Homo
Where to start?
Earth’s timescale: 4.55 billion yrs – a big number
Eons Eras Periods
Stratigraphy and Geologic Time
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!
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.
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
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
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
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
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
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?
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
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
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
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 7
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- How do we know about Earth in the Precambrian?
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- 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�
- Slide Number 41
- Amino acids formed in simulated early Earth atmosphere�
- Early Organisms�
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Stratigraphy and Geologic Time
Eons Eras Periods
Stratigraphy and Geologic Time
Early Earth: The First 2 Billion Years
First 50 Myr – Earth’s core/layering
Archean Fossils
Archean single-celled micro-organisms
Origins of Life: What is Needed?
Deep-sea hydrothermal vents
Summary: Hadean-Archean – long book with few pages
Archean… Thoughts
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]
(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
Gravitational pull exerted by Earth
requires high-density iron inner core
The whole Earth oscillates after large earthquakes
inner core must be solid
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
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
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
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- Other seismic discontinuities�
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- Stratigraphy and Geologic Time
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- Reading the book (the stratigraphic record)�Main concepts:
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- Radioactivity
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- 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:
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Earth’s Internal Structure
How do we know that the outer core is liquid?
How do we know that the outer core is liquid?
How do we know that the inner core is solid iron?
Earth’s Internal Structure – Summary
Biostratigraphy
Geologic Time