AST 248, Lecture 9 - Stony Brook University · James Lattimer AST 248, Lecture 9. Evidence for Evolution, continued Molecular Evidence { The Unity of Life The code used to translate

AST 248, Lecture 9

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

October 22, 2018

The Search for Intelligent Life in the [email protected]

James Lattimer AST 248, Lecture 9

ZooFari, Wikipedia


Greenhouse Effect

NASAJames Lattimer AST 248, Lecture 9

Greenhouse Effect

I Moon: daily temperature (T ) range-175◦ C (-283◦ F) to 125◦ C (257◦ F)

I Earth: without atmosphere, the glo-bal mean T (GMT) is -1◦ C (30◦ F)

I Earth: with atmosphere, the GMTis 15◦ C (59◦ F)

I Greenhouse gases includeH2O (36-70%), CO2 (9-26%),CH4 (4-9%), O3 (3-7%)

I Greenhouse effect on Venus: +250◦ C

Although H2O dominates, it acts as a positive feedback loop.H2O concentration is directly tied to T through evaporation/condensation. When something else (e.g., CO2) causes a Tincrease, more H2O evaporates and enhances the T increase.


Carbon Cycle

NASA Earth Science EnterpriseJames Lattimer AST 248, Lecture 9

Global WarmingI Studies of ice core samples have shown there to be a high

correlation between temperature and CO2 abundance inthe atmosphere, and that CO2 levels are higher now thananytime in last half million years.


Global WarmingI Studies indicate that the rise in CO2 occurs an average of

800-2000 years after the rise in temperature begins.I Thus, a rise in CO2 does not initially trigger global warming.

However, 800 years is very short to typical CO2 cycles(around 100,000 years) so that doesn’t prove CO2 increasesdon’t also lead to further global warming.

I Climate models show enhanced CO2 leads to higher GMT.I If rising CO2 was a result of rising GMT, concentrations of

CO2 in ocean should be decreasing, contrary to observations.Oceans are also becoming more acidic as they warm.

I Decreasing 13C, 14C and O2/N2 proves that extra CO2 in theatmosphere originates from burning buried or stored carbon.

I Models show that global warming results in a largertropopause and a smaller thermosphere, as observed.

I Rising sea levels and more violent storms predicted: observed.I Potenial exists of releasing CH4 from melting Siberian tundra.


Southern hemisphere CO2

concentration trails northernhemisphere (primary source)concentration by about 5ppm.

84% of additional CO2 is from burningfossil fuels, 10% from deforestation,5% from cement production and otherindustries, 1% from volcanic activity.

Life prefers 12C, so release of fossil Cdecreases 13C in atmosphere. Fossil Clacks 14C, which also decreases inatmosphere. Living plants do contain14C, so decrease in 14C/12C cannot bedue to brushfires.

The decrease in the O2/N2 ratioparallels the decrease in 13C since O2 isconsumed by burning fossil fuels.

Oceans are becoming more enriched inCO2, but the opposite would occur ifthey were outgassing it.


Historic CO2, pH and Carbon Isotopic Ratios

Bohm et al. 2002

bomb spike

Manning & Melhuish 1994


Long-Term Climatic Change

I The carbon cycle is a thermostat, but is not always stable, itcan be driven to instability.

I Cooling episodes may be connected with removal of methane,a powerful greenhouse gas, from the early Earth atmosphere.

I This leads to periods of intense glaciation, called snowballearths, when ice sheets covered virtually the entire planet.

I Continuous volcanic activity and decreased erosion increasesatmospheric CO2, leading to runaway heating.

I Hothouse earths are accompanied by dramatic growths in themagnitude and diversity of life, perhaps leading to thedevelopment of eucaryotes and multicellular animals.

I Major snowball earth episodes identified:

I 2.2 Gyr ago (Makganyene)I 710 Myr ago (Sturtian)I 635 Myr ago (Marinoan), immediately precedes the

Cambrian explosion of life.


Evidence for Snowball Earth Episodes

I globalglacialdeposits

I capcarbonaterocks,indicatinganomalousoceanchemistry. W. T. Hyde, T. J. Crowley, S. K. Baum

and W. R. Peltier, Nature 405, 425 (2000)

glacial deposits↓

ca. 650 Myr ago

I increased C13/C12 ratios are consistent with deep freezesthat killed off most photosynthetic life in the oceans.

I associated banded iron formations indicating anoxia(depletion of oxygen) in oceans.


Snowball Earth Episodes

atropos.as.arizona.edu/ariz/teaching/a204


Preservation of Atmosphere

Atmosphere can be lost

I thermal escape

I giant impacts

I solar wind e.g. Mars

Requirements for planetarymagnetic field

I abundant Fe

I molten interior

I convection

I rapid rotation


Major Extinctions

R. A. Rohde and R. A. Muller, Nature 434, 209 (2005)James Lattimer AST 248, Lecture 9

Importance of Oxygen in the Atmosphere

750 Myrs ago, oxygen levels rose from less than 0.1% to 1% ofpresent values (Sturtian).

The snowball earth episode ended with a temporary spike inoxygen, leading to large Edicarian animals by 580 Myrs ago.Life was dominated by cyanobacterial microbial mats. Animalshad limited mobility and were not carnivores.

542 Myrs ago, Edicarian animals became extinct andCambrian explosion ensued.

This seems to be connected with oxygen suddenly crossing,perhaps temporarily, an ecological threshold.

Animals became highly mobile, and evolved legs, compoundeyes, gills and jaws. These were clearly carnivorous.

The key seems to have been the emergence of predators.


The Cambrian Explosion

Hallucigenia

(Burgess Shale)

Wikipedia


Cambrian Explosion



What is the Definition of LifeOrganization or Order Cell structures formed from specific molecular

patterns.

Homeostasis Regulates its internal environment to maintain a stable,constant condition.

Growth and Development Directed by heredity. Organism increases insize of its parts, doesn’t just accumulate mass.

Reproduction Cells divide both to make new organisms and new cells forgrowth. Some can’t reproduce – mules. Others, likeviruses and prions, don’t reproduce by themselves.

Metabolism or Energy Utilization To create and maintain patterns oforder, to reproduce, and to grow. Energy used to counterincreasing disorder mandated by 2nd law ofthermodynamics.

Response to Environment or Stimuli Capable of responding toenvironmental changes or stimuli (touch, light, sound),involving active responses such as motion.All necessary but not sufficient

Evolutionary Adaptation Permanent changes carried by heredity toevolutionary pressures, resulting in positive adaptationsand entirely new species. Sufficient


Evolution of Evolution

I Anaximander (Greek, 610-547 BC) – simple life originally arose inwater and gradually evolved to more complex forms.

I Empedocles (492-432 BC) – suggested creatures poorly adapted totheir environment would perish, foreshadowing adaptation.

I Aristotle – maintained that species are fixed and non-evolving.Eventually became view adopted by the Church andfundamentalists.

I Jean Lamarck (1809) – fossils represent extinct ancestors of living

species.I Organisms possess a built-in drive for perfectionI Organisms can adapt to circumstancesI Simple organisms spontaneously created, evolve to greater

complexityI Organisms inherit characteristics acquired by ancestors


Evolution of Evolution, continued

I Charles Darwin and Alfred Wallace (1850) – Suppliedevidence for evolutionary changes and put forth a modelof how evolution occurs (natural selection).I Populations have the potential to overreproduce, leading

to scarcity of resources, and competition for survival.I Individuals within a population vary in many heritable

traits, some of which make them more competitive.I These lead inescapably to unequal reproductive success

among individuals, the population ultimately becomingprogressively populated by the more competitiveindividuals.

I The biological environment is not static but evolving.I Similar organisms are related, descend from a common

ancestor; all life forms are descendent from a singlecommon ancestor. Darwin tree

I Evolutionary change is the result of natural selection.I Evolution is gradual and continuous. Here Darwin was

heavily influenced by Charles Lyell’s Principles of Geology.


Evidence for Darwinian evolution

I Galapagos Islandfinches

I giant armadillofossils in Brazil

I selectivebreeding:mustard intobroccoli,cauliflower,cabbage, brusselssprouts, kale andkohlrabi; dogs

On the Origin of Species – Darwin

Darwin Tree


Modern Synthesis with GeneticsI Evolution is the cornerstone of modern biology, and is a fact – defined

as “confirmed to such a degree that it would be perverse towithhold provisional consent” – not a theory.

I In evolution, the whole population, not individuals, is what counts.Evolution is a change in the gene pool of individuals over time.

I Variations in individuals are caused by genetic differences.I Populations are collections of individuals which evolve.I A single organism is never typical of an entire population; individuals

do not evolve – populations evolve.I Genes can change between generations because of sexual reproduction

and mutations.I When mutations first occur, they are not adaptive because most

mutations are detrimental. The short-term effect of mutations isminimal or nil.

I Longer-term, the accumulation of mutations and random shuffling ofgenes through reproduction or migration from another populationprovides the source of variation in a population.

I Natural selection controls the direction, rate and intensity of evolution.I Sudden, catastrophic environmental changes can force a speed-up of

evolution.I The only scientific controversy surrounding evolution is exactly how it

occurs, not if it occurs.James Lattimer AST 248, Lecture 9

Evidence for Evolution

Fossil Record – Paleontology Fossil record provides consistentevidence of systematic change through time–of descentwith modification. It can be predicted that no reversalswill be found in future paleontological studies.

Common Structures – Comparative Anatomy Scientists callstrikingly similiar structures in varied species homologiesand have concluded that they are best explained bycommon descent

Distribution of Species – Biogeography Simultaneous wide diversityand specialization. Geographical isolation (Hawaii,Australia, Galapagos)

Similarities During Development – Embryology Ontogenyrecapitulates phylogeny: Although discredited in detail, ifa structure pre-dates another structure in evolutionaryterms, then it also appears earlier in the embryo. Relatedspecies typically share the early stages of embryonaldevelopment and differ in later stages. A wide variety oforganisms from fruit flies to worms to mice to humanshave very similar sequences of genes that are active earlyin development. The cerebrum in humans, the mostsophisticated part of the brain, develops last.


Evidence for Evolution, continued

Molecular Evidence – The Unity of Life The code used totranslate nucleotide sequences into amino acidsequences is essentially the same in all organisms.

The same amino acids and proteins are universallyused.Metabolism is universally carried out by theATP-ADP cycle.

Hemoglobin and myoglobin, among others,sequencing shows family trees identical to thosederived from paleontology and anatomy. Geneticsequencing and molecular clocks reinforce this.

Pseudogenes, which are remnants of genes thatno longer function but continue to be carriedalong in DNA as excess baggage (junk DNA).Pseudogenes change through time, as they arepassed on from ancestors to descendants,reconfirming other observations.


Catastrophism vs. UniformitarianismI Georges Cuvier argued for catastrophism on the basis of geological

evidence (canyons in southern France).I Charles Lyell debated in favor of gradualism, partly because of the

negative religious fundamentalist connotations of catastrophism(e.g., biblical flood). Lyell was trained as a lawyer, and won debate.

I Darwin was heavily influenced by Lyell and his own observations ofgradual changes in finches, etc.

I Fossil record in early 19th century was very limited; the missingpieces were thought to be due to incomplete sampling rather thanbeing evidence for rapid changes connected with extinctions. Nowthat the fossil record is much more complete, evidence forcatastrophies is more obvious.

I Abundant evidence has accumulated to indicate that evolutionproceeds in spurts and starts rather than gradually – thePunctuated Equilibrium Theory of Eldridge and Gould posits thatthe dominant evolutionary changes, involving both extinctions andoriginations, occurred during very short violent catastrophic events.I Mass extinctions at boundaries between geologic eras: Permian

250 Myr BC, Cretacious/Tertiary 65 Myr BC.I Sudden originations of several families of animal types during

the Cambrian explosion 540 Myr BCI Thought to be caused by impacts, supernovae, plate tectonics,

development of Earth’s magnetic field, oxygenation of atmosphere.James Lattimer AST 248, Lecture 9

Principal Creationist ObjectionsEvolution is just a theory. Scientist’s use of theory is different than

general public. Gravity is a theory, but is essentially a factfrom observations.

There are no fossil intermediates – missing links. Darwin worriedabout gaps in the fossil record. Since then most fossilintermediates in vertebrate evolution have been found.Invertebrate fossils are much rarer; gaps are expected.

Intelligent design – life is too complex. The intermediates in theevolution of the ear and eye are observed. Complexstructures evolved as a progression of slight improvements.

Evolution violates 2nd law of thermodynamics. The 2nd law reallysays: disorder increases in a closed system; the Earth isnot. Solar energy is received and the Earth reradiates it.

Proteins are too improbable. Hemoglobin has 140 amino acids.Probability that first one would be leucine is 1/20, andthat all 140 would be the ones they are by chance is(1/20)140 = 7.2× 10−183, an impossibly rare event.Statistical foolishness: You cannot use probability to arguebackwards. The probability that everyone in a class of 50would have the birthdays they do is (1/365)50

= 7.6× 10−129.


Natural selection does not imply evolution. Microevolution(evolution within a species) seems to be themechanism that has produced macroevolution(evolution among species). Man-made selectionsalone are remarkably distinctive: dachshunds,chihuahuas and greyhounds; mustard andcauliflowers.

Irreducible complexity. If each part of a complex process likeblood clotting is essential, how can naturalselection fashion any one part?What’s wrong with this argument is that eachpart of a complex molecular machine evolves intandem as part of the system. Blood clottingevolved from a much simpler system whichoriginated 600 Myrs ago in lampreys, the mostprimitive fish. Proteins were incorporated 100Myrs later in the first vertebrates. 50 Myrs laterclotting triggered by contact with jagged surfacesevolved. Mammalian clotting now relies on allthree components and can’t act independently ofany of them.


Evolution and Belief






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AST 248, Lecture 9 - Stony Brook University · James Lattimer AST 248, Lecture 9. Evidence for Evolution, continued Molecular Evidence { The Unity of Life The code used to translate