Lithosphere, Earth’s crust and Aesthenosphere, molten layer on which lithosphere floats, and lithospheric plates move.
1) Aesthenosphere from Aesthenes, Greek, - weak. Aesthenosphere, mechanically weak, deforms easily and viscously. Seismic waves have low velocity, so easily identified in seismographs. Layer suspected by 1920s, but not confirmed until
Chilean earthquake in 1960.
2) Lithosphere (rocky) crust. Density of crust varies, continents low density, oceanic high density. Deforms elastically (can recover previous shape) and through brittle failure → earthquakes. Both spheres postulated prior to plate tectonics.
VG
3) Geologic time – a) Herodotus, 5th century B.C., found fossil shells far inland in what are now parts of Egypt and Libya, he inferred the Mediterranean Sea had once extended much farther to the south. Few believed him, although he was correct. b) Relative time, principle of superposition. Material is deposited forming layers with the youngest material at the top and the oldest at the bottom.
Principle holds but can be confused by lifting and tilting of the crust near plate boundaries and mountain ranges. 1785-1800 first proposed by James
Hutton, Scottish Geologist, and William Smith English surveyor who realized that layers of rock underground were continuous from outcropping to outcropping and could be identified by their fossils. With the fossils providing a crude times scale →
Map that Changed the World .
Thus the fields of petrology (rock formation), stratigraphy (studies of layers) and paleontology (life) merged to read the tattered pages of the
Earth’s crust, lithosphere, (
Origin of Specie s, pp 316). Thus ancient seas and mountains could be uncovered and the relative ages of the events deduced. c) Radiometric or absolute time, determined by natural radioactive decay of various elements. 1896 Henry Becquerel, the French physicist, decay of
Uranium, 1905, Rutherford--after defining the structure of the atom-- made the first clear suggestion for using radioactivity as a tool for measuring geologic time directly; 1907, Professor B. B. Boltwood, radiochemist of Yale University, published a list of geologic ages based on radioactivity. showing that geologic time would be measured in terms of hundreds-to-thousands of millions of years. These dates would be later revised with precise dating beginning in the 1950s. d) Parent. P = P o
e
P = P•(e
λt
-λt
, def of radioactive decay. Daughter, D = P o
– P = P•e
λt
–
- 1), where λ is the decay constant given by t
1/2
= ln(2)/λ. Then an age can be determined from t = 1/λ • ln(1+D/P). e) The following are the common elements used for aging.
Lecture notes, Terry Deshler, University of Wyoming Page 1

Parent Isotope
Samarium-147
Ru-87
Th-232
U-238
K-40
U-235
C-14
Stable Daughter
Neodynium-143 106,000
Strontium-87
Pb-208
Pb-206
Ar-40
Pb-207
N-14
Half life x
1e6
48,800
14,000
4,500
1,250
704
0.006 f) Technique relies on measuring precisely D and P precisely, difficult when
D or P are small. i.
K → Ar used for all ages of rocks known. Useful only on igneous rocks, not sedimentary or fossils. Potassium is a common element found in many materials, such as micas , clay minerals , tephra , and evaporites . In these materials, the decay product 40 Ar is able to escape the liquid (molten) rock, but starts to accumulate when the rock solidifies ( recrystallizes ). Time since recrystallization is calculated by measuring the ratio of the amount of
40
Ar accumulated to the amount of
40
K remaining. ii.
C-14 useful for recent paleontology. Earlier sediments/fossils dated by using relative scales tied to a layer of igneous rocks. g) Other isotopes can be used for temperature, particularly
18
O and
13
C. The data are presented as isotope ratios with respect to a standard. Thus δA = r
A
– r
As
)/r
As
, where r
As
is a standard ratio of two isotopes and r
A
is the measured ratio. Thus δ 18
O = (r
18
O – r
18s
O)/r
18s
O, where r
18s
O =
18
O/
16
O =
1/498.7 for “Vienna standard mean ocean water”, and r 18
O =
18
O/
16
O is the measurement. The notation % o
= 0.001, similar to % = 0.01, although % o is referred to as “per mil”. h) The equilibrium distribution between two substances (water/vapor or water/mineral) depends on the fractionation factor, f
1,2
. Thus 18 O/ 16 O v
= f v,w
18
O/
16
O w
for the difference between
18
O/
16
O in water and vapor which are in equilibrium. In this form f v,w
will be < 1 and approach 1 as temperature increases. These present powerful temperature proxies. i)
δ 18
O = (r
18
O – r
18s
O)/r
18s
O i.
r
18s
O =
18
O/
16
O ~ 1/500 normally in sea water. As T cools the heavier isotopes are less likely to evaporate and more likely to condense. Thus over long times δ 18
O sea water becomes less negative (increases) and glacier ice δ
18
O becomes more negative
(decreases).
1.
δ 18
O (273) = -11.7% o
2.
δ 18
O(290) = -10.1% o
3.
δ 18
O(350) = -6.0% o
Lecture notes, Terry Deshler, University of Wyoming Page 2

ii.
But this requires samples of the seawater or glaciers.
1.
Ice cores give record for last 0.6 Ma.
2.
Foraminifera (forams) shelly amoeba builds shells from
CaCO
3
calcium carbonate, thus capturing the δO
18
present in the seawater at the time of formation. Forams appear
0.525 Ga but the best record is only last 70 Ma. a.
Planktonic – live near surface (planktos ≡ drifting) b.
Benthic – at the sea floor. More reflective of global climate. Temp near 0ºC. j)
δ 13
C = (r
13
C – r
13s
C)/r
13s
C i.
Photosynthetic life prefers
12 C → shales enriched in 12 C → life present. This enrichment is also transferred to heterotrophs dining on the photosynthetic organisms which can fix Carbon
1.
δ 13
C (outgassing volcanoes, upper mantle) = -6% o
2.
δ 13
C(for CO
2
in atmosphere) = -8% o
3.
δ 13 C(fossil fuel) = -32% o
4.
δ 13
C(methanogenesis) = -50% o
fixing carbon from CH
4
.
4) Age of Earth – cannot be determined by rocks on Earth since all have been recycled through molten core, thus losing their original information. a) The oldest rocks: 1) the Acasta Gneiss Complex near Great Slave Lake,
Canada -- 4.03 Ga, 2) the Isua Supracrustal rocks in West Greenland -- 3.7 to 3.8 Ga, 3) Swaziland (3.4-3.5 billion years), and 4) Western Australia
(3.4-3.6 billion years). These rocks are from lave deposited in shallow water not from Earth’s crust. Zircon (ZrSiO
4
→ δ
18 O is available →
Temperature) crystals with ages of 4.3-4.4 Ga found in younger sediments, but rock origin of zircon not known. b) The best age for the Earth (4.54 Ga) is based on old, presumed singlestage, leads coupled with the Pb ratios in troilite (FeS) from iron meteorites, specifically the Canyon Diablo meteorite. Claire Patterson, 7 years into mid 1950s to get the final number due to contamination of laboratory samples from atmospheric lead from leaded gasoline. Long campaign by Patterson led to clean air act, 1970 and banning leaded gasoline in 1986. Mineral grains (zircon) with U-Pb ages of 4.4 Ga have recently been reported from sedimentary rocks in west-central Australia.
The assumption is then that the meteorite has not been altered since its formation at the dawn of the solar system and the Earth also dates from that time. Oldest Moon rocks date from this same period, although younger ones also found.
5) Geologic periods on Earth into deep time (1.3) VG – Geologic time a) 4.5-3.8 Ga – obscure, T 200-500 K from volcanism and heat from interior.
Early “solar abundance” atmosphere lost. Zircon crystals 4.4 Ga show evidence of contact with water, so a crust was forming at this time and
Lecture notes, Terry Deshler, University of Wyoming Page 3

would have interrupted the flow of heat from interior. Heavy bombardment also causes warm T. b) 3.8 Ga, oldest rocks – Greenland, end of Hadean, open water, organic carbon, prokaryote – stromatolites? Other explanations w/o life possible.
Not a snowball earth. c) 2.6 Ga – proterozoic, cherts (H
2
O and SiO
2
) → δ 18 O → chert paleothermometer. Record indicates T = 70 → 30 C (350→300 K), also glaciation, first independent evidence of life and undisputed evidence of cyanobacteria and other prokaryotes (cell has no nucleus). Diamictites – material transported by floating ice. d) 2.3 Ga – global glaciation probably. Rocks impacted by glaciers formed at
12º latitude based on ferrous crystal orientation. Big O
2
event. e) 1.8 - 0.8 Ga no evidence of glaciation. Eukaryotes appear. Greenhouse gases changing. Oxygenation begins towards end of proterozoic. This requires burying the organic carbon, otherwise it would be reverted to the atmosphere through the decay by bacteria of the organic carbon. Climatic variations small (“big yawn”). Evidence of O
2
from participation of isotopes of sulfur,
32, 33, 34, 36
S in various reactions. There is mass independent fractionation only in absence of O
2
. f) Snowball earth at 0.7 Ga, then climate moderated between ice free and some ice present, but never reverted to a snowball Earth after the 0.7 Ga event in the neoproterozoic. g) 0.7 end of neoproterozoic. , multicellular (metazoans) life appears, medusa, 0.5 Ga Cambrian explosion all phylums now in existence make their entry at this time, while others appear and become extinct. What precipitated the Cambrian explosion? Still unsolved. Flow of carbon – land and marine carbonates, dissolved organic and inorganic carbon in sea water, atmospheric CO
2
. Mass extinction at end of Permian, 96% of all marine and 70% of all terrestrial animals extinct. h) Last 70 Ma ice free for 35 Ma – glaciation then rebound. Paleo/Eocene thermal maximum. Extinction of benthic forams (water too warm).
Hothouse from CO
2
released from clathrate, CH
4
.
13
C severely depleted.
Bolide impact at the Cretaceous/Tertiary (K/T) boundary, 65 Ma → end of dinosaurs.
6) Plate tectonics – a) Alfred Wegner, German geophysicist, meteorologist, trained astronomer but preferred meteorology and climatology. Balloonist, pioneered weather balloons, winter in Greenland, recovered ice core to 25 m. Died in 1931 on
Greenland resupply mission (50 and a smoker). b) Proposed continental drift in 1912 by comparing e.g. coasts of South
America to West Africa and India and Madagascar to East Africa. But he
Lecture notes, Terry Deshler, University of Wyoming Page 4

could not find a mechanism, so theory not accepted, although he showed the rocks on the continental boundaries of Africa and South America were similar and proposed that mid ocean ridges might be evidence. US geologists organize conference in opposition. c) 1950s paleomagnetism. 1953 evidence indicated that India had been in southern hemisphere as predicted by Wegener. 1960s sea floor spreading confirmed. Alternating alignment of ferrous crystals in mid Atlantic ridge consistent with paleomagnetic shifts of N and S magnetic pole. Iron crystals in lava align with Earth’s magnetic field. Wegener recognized as the father of one of the revolutionary scientific theories of the 20 th
century. d)
Earth’s magnetic field – Present south magnetic pole of Earth in north →
N end of compass is attracted to S magnetic pole. Magnetic fields arise from Ampere’s law ( ) while electric fields arise from Faraday’s law ( ). It is thought there is a current in the liquid outer core spinning with the Earth. Origin of current?
Motion of Earth in a magnetic field? Chicken and egg problem. Reversals of poles occur due to large disruptions in the chaotic flow in the liquid outer core, where convection, Coriolis forces play large roles. e) Lithosphere two types of crust, oceanic, more dense, and continental crust, less dense. f) Plate tectonics still in the realm of kinematics – motion can be described but driving forces still point of serious research. Three basic ideas i.
Mantle dynamics – convection in the upper mantle ii.
Gravitational secondary forces coupled with convection iii.
Earth rotation related forces – tidal forces (initially proposed by
Wegener). VG – plate tectonics
7) Super continents a) Importance of continents to climate i.
Platform for glaciers ii.
Silicate weathering → CO2 abundance in atmosphere. Abundance dependent on the extent of weathering iii.
Influence the transport of heat by the oceans as continents move. iv.
Habitat for life. b) Columbia (2.0 Ga) proposed 2002 – evidence in Columbia river drainage c) Rodinia, (motherland in Russian), 1.2-0.75 Ga, first supercontinent about which we have undisputed evidence, most mass low latitudes, NH d) Pangaea (0.3 Ga) Phanerozoic i.
Gondwanaland – southernmost land mass split from Pangaea about
0.2 Ga. VG – super continents
Lecture notes, Terry Deshler, University of Wyoming Page 5

(Venus, 97% CO2, 2% N2 and less than 1% of O2, H2O and CH4 (methane)
Earth Venus Mars
N
2
0.79 2 3 x 10 -4
O
2
0.20 < 0.001 10 -7
Ar 0.01 0.005 2 x 10 -4
CO
2
0.0003 64 0.009
H
2
O ~ 0.02 ~ 0.01 ~10 -6
Total 1.00 90 0.01
8) Impact on life a) Origin of life – i.
Ambiguous evidence
1.
3.46 Ga old chert in NW Australia - single celled organisms –cyanobacteria?
2.
Older rocks in NW Australia (3.51 bya),
3.
3.0 bya South Africa \
4.
Oldest known rocks, 3.85 bya banded iron outcrops on the island of Akilia - SW coast of Greenland.
5.
All have been used by paleontologists to stake claims to evidence of life. a.
Some bacterium like structures. b.
Others Greenland samples (3.85 bya) from isotopic
12
C /
13
C ratios. In all samples
12
C enhanced, but there are non-biological pathways, to the same ratios → numerous challenges.
6.
Although intriguing structures all cases alternate explanations, not involving life, are also consistent with the observations. The timing of the origin of life is open. ii.
Unambiguous evidence in:
1.
1954 cherts of the Gunflint formation in NW Ontario fossils of 2 Ga bacteria from an iron rich sea. Fossil record revealed cyanobacteria and iron metabolizing bacteria, difficult to find today. There were large atmospheric changes occurring about 2 Ga as the cyanobacteria production of oxygen was beginning to cause iron in the oceans to precipitate → iron metabolizing and anaerobic bacteria driven underground.
2.
Even older fossils can be identified by a biomarker molecule, hopane a 5 ring organic, found in a petroleum like residue representing the remains of marine algae. Such droplets of residue were found in 2.7 Ga shale, the Pilbara
Craton in W. Australia. The primary job was to rule out any sort of contamination and to establish that these 2.7 byo rocks had never experienced temperatures that could have destroyed the hopane, i.e. temperatures had to remain
Lecture notes, Terry Deshler, University of Wyoming Page 6

below ~300

C. This done the results were published in
1999 (Summons).
3.
A second paper at the same time announced results from nearby 2.5 Ga remains which contained a hopane variant indicative of cyanobacteria. Cyanobacteria, dominant organism on the planet for a period exceeding by a lot even the reign of the dinosaurs. b) Cyanobacteria i.
thrive in coastal habitats, characteristic of the geologic formations in which they have been discovered, particularly chert, created in coastal environments as silica is precipitated. ii.
Tidal flat cyanobacteria must survive desiccation (low tide), then osmotic trials when submerged. → cyanobacteria secrete an extracellular envelope to protect cells inside. This shell can be fossilized. iii.
Importance not from shells, nor that they have existed unchanged since the end of the Archean Eon, 2.5 Ga, if not early Archean
Eon, 3.5 Ga, nor that they were dominant organism for 1 Ga/ iv.
Their importance in ability to photosynthesize and gain energy and fix carbon. → three impacts of immense proportions.
1.
Primary producers of organic molecules in proterozoic oceans and coastlines for 2 by.
2.
Excreted oxygen as a byproduct of photosynthesis thus creating the oxygen dominated atmosphere of today and providing the opportunity for a new form of metabolism, respiration, to become dominant. Thus leading eventually to land animals and predation.
3.
Best trick of all, to merge with another single celled organism to form a new organism and begin a whole new branch on the "tree of life".
4.
In 1905 Russian, Mereshovsky (Kazan Univ), tried to explain two observations: 1) the late 19 th
century German botanist, Schrimper, showed that chloroplasts grow and divide independently from the cells surrounding them, although in synchrony with those cells, and that chloroplasts lost from cells cannot be generated anew.
Chloroplasts spring only from chloroplasts. 2) Corals and some other animals harbor symbiotic algae in their tissue.
Mereshovsky's hypothesis was that cells of algae and plants are made of two independent organisms, with the seat of photosynthesis, the chloroplast, originating as a cyanobacteria, perhaps originally swallowed by a protozoan. Thus the chloroplasts thrive (grow, synthesize
Lecture notes, Terry Deshler, University of Wyoming Page 7

proteins, and hand down their characteristics, all independent of the nucleus. They are symbionts, not organs. Thus eukarya could have originated as endosymbionts (two cells nested one inside the other in mutually beneficial partnership) Suggestion was discussed vigorously, then faded, not because of refutation as much as neglect, and inability to answer a number of fundamental questions. How did the symbiont become established? How did it fall under the genetic code of the nucleus? How did it escape digestion?
5.
By the 1960s in textbooks the idea was mentioned as a failed hypothesis. In 1967, in a paper rejected 15 times,
Lynn Marguls (formerly Lynn Sagan) reinvented this hypothesis (without knowing of Mereshovsky) as the origin of eukaryotic cells, proposing as Mereshovsky that chloroplasts originated as endosymbiotic cyanobacteria, and that mitochondria (the sites of respiration for eukarya
(animals) which respire) were descended from respiring bacteria. This idea was and is a shock for the Darwinian world view that evolution is a process of branching from a common ancestor. Now added to the mix is the idea that branches could fuse as well. modern tools show cyanobacteria and chloroplasts share a common structural organization, are nearly identical in details of photosynthesis, and chloroplasts respond as bacteria to antibiotics, not like the nucleus or cytoplasm, and contain their own DNA, RNA. chloroplasts in red and green algae, and their descendants (plants) are surrounded by two membranes. One manufactured by the surrounding cytoplasm and nucleus, and the second made by the chloroplast itself. Thus the chloroplast actually lies outside the cell.
6.
The final evidence came from genetic sequencing. The gene sequence from chloroplast DNA is closer to cyanobacteria than to the nucleus of the genes in which they reside. So the green world surrounding us is evidence of blue green bacteria still dominating our world by tagging along on a protozoa. The details of how one cell can become an integral part of another and not be digested have been worked out. Similar results have been found in similar detail as mitochondria were investigated. In this case the first such proposal was made in 1925 (Wallin, U Colorado), but as Mereshovsky faded into oblivion before being resurrected by Marguls (again unknowingly). Thus these
"failed hypotheses" have become our new understanding of the basis for critical junctures in the tree of life.
Lecture notes, Terry Deshler, University of Wyoming Page 8

v.
Thus these bacteria, nearly invisible to the unaided eye, coupled with another bacteria that could respire, have very literally laid the basis for the macroscopic world of plants and animals that we know. c) Cambrian explosion i.
No sharper or more confusing boundary in geologic time. ii.
Discovered in the early 1800s in Wales (Cambria) when multicellular animals suddenly dominate the fossil record. iii.
Basic facts
1.
Prior to 0.7 Ga ago, 3.8 Ga after the Earth’s formation, 3.1
Ga after unicellular prokarya, and 1 Ga after unicellular eukarya, There is no evidence for multicellular animals in the fossil record.
2.
Then in the space of 0.1 Ga all major Eukarya phyla (about
30 depending on who’s counting) of today’s world appeared, including many other phyla which have since disappeared.
3.
Skeletonized protozoa appeared nearly simultaneously in many clades. iv.
How could this have happened? Wasn’t life a slow progression of slight variations, some to success, more to failure, in life’s battle for survival, with the successful leading to further variation and more specialization. Darwin recognized the challenges to his theory that the Cambrian boundary presented. d) Fossil record little disparity dating appearance of significant multicellular life. Below this level the strata are devoid of fossils, above they are filled, and are not constrained to a handful of geographical locations. They are global. Eukarya appear to extend approximately 1 by prior to the
Cambrian period, late compared to the prokarya and archea. The evidence for multicellular eukarya prior to the Cambrian boundary, however, is primarily limited to megascopic algae, and perhaps seaweed. How could it happen so fast and be so complete. There are a number of hypotheses, of which I’ll mention just a few. i.
There was no radiation, but this period was preceded by a long
(200 my) period of development of small metazoans which left no fossil trace, hidden evolution. ii.
An environmental barrier, did not preclude a large variety of
Eubacteria, Archeabacteria, and megascopic algae, even seaweed, but did preclude large animals. An anoxic atmosphere would not support respiration or limit exposure to UV. Most life up to this point was anaerobic. Larger animals needed a more efficient way
Lecture notes, Terry Deshler, University of Wyoming Page 9

to burn energy, but where would the oxygen come from? A global geologic event could provide it and did occur in this time frame.
Rodinia torn asunder in the late Proterozoic, just pre-Ediacaran. If massive rifting and extensional basin formation buried large amounts of carbon, from extensive algal mats covering the sea floor, the buried carbon could allow high rates of oxygen formation. The natural cycling of oxygen back to water and carbon dioxide, from creation during photosynthesis, is lost if the carbon is buried. iii.
But why such a wide diversity, forming all existent phyla in less than a few hundred million years, with no new phyla appearing since then, and forming a number of phyla which have disappeared from the record. Perhaps as metazoans appeared all ecological niches were available for population. No competition for the resources. Peak hopping example.
Sources:
Pierrehumbert, R. T., Principles of Planetary Climate, 2011, 1.7-1.10
On the orgin of life deDuve, 2005, Singularities , QH 325.d418
Hazen, 2005, R. M. Gen-e-sis, the scientific quest for life's origin , QH 325.h39
Knoll, A., 2003, Life on a young planet . QH325.k54
Thomas PJ, Kicks, RD, Chyba, CF, KcKay, CP, 2006, Comets and the origin and evolution of life . QB721.c6485
Of note:
Organic life beneath the shoreless waves
Was born and nurs'd in ocean's pearlly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing. (Erasmus, Darwin, 1804)
Lecture notes, Terry Deshler, University of Wyoming Page 10