The final exam is semi-cumulative. It will emphasize the material covered in class since the last exam, but will also include some questions from the first two thirds of the class. Approximately 100 points will be from the last third of the class (i.e., since the last exam) and 50 points will be from the first two-thirds of the class.
This study guide covers only the last third of the class material. Review posted class notes, handouts, your
own lecture note, the study guide for
exam 2 and exams 1 & 2 for material before the second exam.
Readings: 1. Assigned readings #4,5,6 & 7. Available via the course website
(http://www.geo.arizona.edu/geo3xx/geo308/) on e-reserve
2. Lecture notes posted on web
3. Handouts given in class.
You can count on the question about the Geologic Time Scale, one or more questions from previous exams, some calculations, some graphs, some data to interpret, and some questions from the readings (even if I didn’t talk about the reading in lecture).
1. Dating with growth rings: trees (dendrochronology); corals or clams (sclerochronology)- matching of distinctive rings in different trees (or corals or clams) to extend chronology
2. Radiocarbon. 14C, a naturally produced radioisotope of carbon; half-life of 5,730 years
incorporated into living matter (wood, plants, bone, shell); after death, no new 14C added; amount already there decays. Proportion of 14C remaining is an estimate of time-since-death (age before present). Technique useful to maximum of about 40,000 years.
a. Corrections for variation in production rates is done by cross-dating with tree-rings. b. Correction for “reservoir effect” (storage of old carbon) in oceans done by dating historic collections.
3. Amino acid dating (shell, bone, wood) --change in proportion of alloisoleucine to isoleucine after death (A/I ratio). low A/I => young; high A/I => old; BUT rate of change depends on temperature, therefore regional calibration required to get estimate of absolute age; otherwise age estimates are relative. Advantages: low cost, speedy results.
Lithostratigraphy - subdividing rocks based on their lithology; Formations = mapable lithologic
units.
Biostratigraphy - subdividing rocks based on their fossil content; Zones - strata that contain
diagnostic fossil species
Correlation-- determining temporal equivalence- rocks deposited at same time.
1. Time-correlation using physical evidence: isotopic dating, distinctive marker beds such as ash falls, position in transgressive/regressive cycle, varves – distinct sequences of annual sedimentary layers
2. Time-correlation using fossils: Stratigraphic ranges controlled by evolution: time of first appearance (approximates time of origin) and time of last appearance (approximates time of extinction).
Secondary controls on stratigraphic range: environment, migration, quality of record (sampling, unconformities, preservation). These secondary controls cause true ranges to be under-estimated.
-- Single species approaches: "index" or "guide" fossils (short range, wide ecological tolerance, broad geographic distribution; examples: foraminifera, ammonoids)
-- Multi-species approaches: assemblage zones, concurrent range zones, graphic correlation.
3. The development of the Geologic Time Scale
Superposition and early subdivisions based on lithology as devised by Arduino in the late 18th Century (e.g., Primary, Secondary, Tertiary)
William "Strata" Smith and Georges Cuvier subdivided rocks based on their fossil content – around 1800.
Concept of type sections, with relative age based on superposition
Correlation to the type section, using fossils, allows an assignment of geologic age to fossiliferous rocks. Radiometric dating of volcanic rocks within sedimentary sequences allows for assignment of absolute age (in Ma).
Paleoecology: study of the inter-relationships of fossil organisms and their environment.
Objectives:
1. the environment in which the fossil organism lived,
2. the biology of the fossil organism
3. biotic interactions
4. the distribution of the organisms; their biotic communities
1.
Paleoenvironmental reconstruction.
Environmental indicators - physical, chemical, biotic, or taphonomic features that are diagnostic of one or a few environmental conditions.
a. Physical environmental indicators. Sediments and sedimentary structures that can reveal evidence for wave and current energy, subaerial exposure and others environmental features. Some examples of physical environmental indicators:
- mudcracks: subaerial exposure; - raindrop imprints - subaerial exposure
- grain size - indicators of energy. Coarse high-energy; fine low- energy
- ripple marks: wave ripples- symmetrical; current ripples- asymmetrical
- cross-bedding: current energy and direction.
b. Chemical environmental indicators: minerals, chemicals, trace elements and isotopes
Some examples of chemical environmental indicators are:
- oxidation state of Fe in the rocks.
- evaporite minerals or deposits.
- disseminated sedimentary pyrite (Fe2S).
- the mineral glauconite.
Trace elements - slight impurities in composition are often environmentally controlled.
Mg (the trace element) often substitutes for Ca in calcium carbonate, the common constituent of many hard parts. In many cases, the amount of Mg increases with temperature
Stable isotopes: elements that differ in the number of neutrons in their nucleus are said to be different isotopes. Stable isotopes do not decay with time. Example of oxygen isotopes: 16O and 18O are two different isotopes of oxygen. Oxygen sampled from calcite or aragonite hard parts (CaCO3) that make up fossils.
Controls on oxygen isotope composition in marine hard parts:
n Global ice volume: more 16O in continental ice (H216O sheets than in ocean, during ice ages, therefore, the oceans are relatively enriched in 18O
n Temperature: as temperature increases, the amount of 16O in calcite increases.
n Fresh water mixing: Rivers and lakes have relative more 16O (as H216O) than seawater, so freshwater shells have more CaC16O3) than marine shells
transfer ecology - a uniformitarian assumption that the ecology of the living representative is an indication of the ecology of the fossil. Example: reef building corals today occur in clear, shallow, tropical water; fossil reef-building corals probably did so too.
-Taxon-free approach. Example of Jack Wolfe’s study of leaf margins: proportion of leaves with entire margins increases with increasing temperature in modern ecosystems. Used to reconstruct changes in Cenozoic temperatures
-trace fossils. trace fossils are the sedimentary structures made by the activity of organisms. Ichnofacies too.
d. Taphonomic indicators - the taphonomic condition of fossils is often sensitive to environmental conditions; fragmentation, encrustation, orientation.
Substrate and mobility classification: mobile vs. sessile; benthic, planktic, nektic; epifaunal vs infaunal. Give an example of each.
Trophic (feeding) classification: primary producer, suspension (or filter) feeding, deposit (or detritus) feeding, herbivore, carnivore, omnivore, scavenger/ carrion-feeder. Give an example of each
Inferred from
1. transfer ecology - if same species or close relative living today
2. direct evidence - from the actual mode of occurrence in the rocks (munch marks, diet
from dung)
3. analysis of functional morphology – streamlining of body shapes, tooth shapes.
Example: Hansen’s analysis of Ground Sloth dung deposits from the Grand Canyon: was there a change in diet that caused their extinction?
3. Biotic interactions Many biotic interactions often leave little or no direct evidence in the fossil record. Munch-marks, drill holes, etc.
Historical ecology - reconstructing not-so-ancient environments to provides baseline against which to measure the human impact on the environment.
Example: Historical ecology of the Colorado River delta: what were conditions like before 1935? Differences in population density and salinity tolerance from oxygen isotopes. Assigned reading #6 or http://www.geo.arizona.edu/ceam/Hecold/hecolcd.htm
Species - biological species definition: groups of populations whose individuals interbreed to produce fertile offspring. - morph. species definition: groups of populations whose individuals are morphologically similar to each other (so similar that they probably interbred).
Evolution - changes in the relative frequency of heritable characteristics that take place from generation to generation.
Speciation – the origin of a new species (can have evolution w/o speciation, but no speciation w/o evolution)
The basic ingredients of evolution: variation & natural selection,
Heritable variation- For evolution to work, that variation needs to be heritable. Eye color, skin color, hair color; Mutations (new variation) do not arise because of some "need" of the organism.
Natural selection. Some of those individuals in the species may, because they possess a heritable characteristic, be more likely to survive to reproductive age, or may be more likely to produce offspring. Natural selection: differential survival and or reproductive success of individuals having particular heritable trait. Survival of the fittest: survival of the sexiest
Types of selection:
1. Directional : shift in mean value. Persistent selection against (or for) one
extreme.
2. Stabilizing: No change in mean value, but a decrease in variation or at least a stable range of variation thru time. Extremes selected against (or mean selected for).
3. Disruptive. Mean selected against, extremes selected for.
Speciation - how to make a species. To the two ingredients of evolution: variation and natural selection, we need to add a third - the interruption of interbreeding.
--Phyletic speciation - the evolution of one species into another thru time. After a number of generations, the first and last of the populations are morphologically distinct enough to earn the title of different species. That is, individuals in the descendant population probably couldn't interbreed with individuals in the ancestral population.
--Branching speciation (cladogenesis- the formation of a new clade (a species in this case) in addition to the existing one. Interruption of interbreeding most often takes place through geographic isolation (called allopatric speciation) though there may be other ways to isolate populations. New species are added and diversity increases. The ancestor may persist along with the descendant.
Patterns of speciation
in the fossil record:
1. Phyletic gradualism. Evolutionary change is continuous and relatively slow. Continuous change with gradual divergence 2. Punctuated equilibrium. Evolutionary change concentrated in relatively short periods of time. Stasis then quick change.
--Current issue is over how frequent one of these patterns
is relative to the other. Which is the
more common pattern of microevolution? Extremes of a continuum?
Three types of extinction:
(1) Pseudoextinction, or phyletic extinction: where one species evolves into another species. There is no loss of species number;
(2) True or terminal extinction: where a species lineage becomes extinct. A loss of species numbers.
(3) Local extinction: a species goes extinct somewhere within its geographic range, but not globally.
Extinctions are commonly measured as the number or % of families that make their last appearance in some time interval. The best record that we have is the marine record.
Two magnitudes of extinction
(1) Background extinction: rate never falls to zero; a relatively low rate of approx. 5 families per million years. Note trend of decreasing background extinctions.
(2) Mass extinction Extinctions in which rates exceed background rates by a factor of two or so, affecting a broad range or organisms (i.e., not confined to one taxonomic group or another or one ecological group or another), and may have been of relatively short duration. That is, they may have been catastrophic, with intervals of time anywhere from a million years down to one bad weekend.
The timing of mass extinctions is often a controversial topic. If mass extinctions are gradual, the catastrophic causes (such as asteroid impacts) are unlikely. If mass extinctions are sudden, then slowly-acting causes (like climate change) are unlikely).
The five groups of high extinction rates in the marine record have come to be known as the "Big Five" 1. Late Ordovician. 2. Late Devonian. 3. end-Permian. 4. Late Triassic. 5. end-Cretaceous.
The end-Cretaceous, or
K/T extinctions:
Impact hypothesis: - that 65 million years ago, the earth was struck by a large asteroid (10 km in diameter). The impact pulverized the asteroid and a good deal of the crust where the asteroid struck. The pulverized debris was injected into the atmosphere, where it blocked sunlight (total darkness for 50 days in one scenario) and rapidly cooled the climate. The darkness shut off photosynthesis, killing the short-lived oceanic phytoplankton, cutting off the food supply of herbivorous dinosaurs. That, plus the cooling, should have been enough to cause the extinctions. Other impact scenarios include acid rain, giant tidal waves, and global wildfires.
Evidence includes: Iridium has been found in other boundary layers in more than 100 sites worldwide: some terrestrial, some marine. In addition, shocked minerals, glass spherules/tektites, soot (carbon black), tsunami beds, impact crater of the right age and right size (200 km) in Yucatan peninsula of Mexico, fossil record consistent with sudden extinction.
Effects of extinction (mass or otherwise, K/T or other times):
Removing incumbents to allow diversification of other groups (e.g., mammal diversification after dinosaur extinction), 2. Chance effects, Extinction a bad luck rather than bad genes. When extinction rates are very high, as during the end-Permian extinction, survival may be result from luck rather than a superior adaptation. 4. Ecological effects: Zombies – the living dead. Species that depended on other species that are now extinct. Example: Calivaria tree and Dodo.
(1) deterministic traits- intrinsic features of species, populations or individuals (these traits are NOT mutually exclusive)
· Geographic Range- Species are better able to survive if they have a large geographic range
· Rarity- If a species is rare (low population size) it is more likely to go extinct
· Degree of Specialization- A species that is highly specialized is more likely to go extinct than one that is a generalist. Take the Calivaria Tree for example, its reproductive success was entirely dependent on the Dodo. When the dodo went extinct, the Calivaria Tree lost its ability to reproduce. With no reproduction, it will perish.
· Population variability- The more variation in a population, the more likely the species will be able to ride out perturbations like disease, introduced predators etc. With increased variation, the species can ‘adapt’ more quickly to changes in their environment
· Trophic Status- The higher a species trophic status, the more vulnerable it is to extinction (i.e. carnivores are more likely to go extinct than herbivores). Carnivores tend to have (a) small population sizes (b) long onset to sexual maturity and (c) produce few offspring in a lifetime. This makes them more vulnerable to extinction...more so than rabbits, which tend to be numerous, reproduce like mad and have large litters of young.
· Intrinsic rate of population increase- This is a metric that captures how well a species is at recovering from some kind of perturbation. If a species can reproduce quickly and efficiently (hence a high intrinsic rate of population increase), then it is more likely to ride out the perturbation and not go extinct
(2) stochastic processes- unexpected events that are due to chance alone (i.e. natural disasters, meteor impacts etc)
· If there were no deterministic factors, stochastic processes would still ensure that all species would go extinct sooner or later....why? Think about the Gambler’s Ruin....
· Gambler’s Ruin ---> HOUSE ALWAYS WINS. Why is that? When you gamble, your money fluctuates quite a lot (lose a little, win a little, lose a lot, win a lot)... but if you play long enough, at some point you WILL eventually lose all your money, guaranteed. Once you hit $0.00, that’s the end of the game.
The story of the heath hen - example of how deterministic factors and stochastic processes can lead to the demise of a species.
The heath hen was a subspecies of the Greater Prairie chicken; therefore it was very tasty and easy to hunt. Even though it had a large geographic range (Virginia to Maine) and was fairly abundant, humans hunted the heath hen to the point where its population declined rapidly and its geographic range decreased substantially.
· By 1840, it was restricted to just a few places
· 1870 on, it was only found on Martha’s Vineyard
· 1908, people became concerned...they built a 1600 acre refuge to save the heath hen. By this time, there were only 50 birds left
· The population steadily increased until 1916 when a series of natural disasters struck Martha’s Vineyard:
- huge fire which spread quickly due to strong winds
- VERY hard winter
- a predatory bird, the goshawk, invaded the area and ate many heath hens
- if the previous disasters weren’t bad enough, the lingering heath hen population was stricken with a poultry disease
· By 1927, there were only 11 males and 2 females left
· In 1928, only 1 bird remained.....it was last seen on March 11th, 1932.
A theory of the universe, earth and life that argues that the Universe and the earth were created by an intelligent, knowing creator a relatively short time ago (on the order of tens of thousands of years), and that the major, basic kinds of plants, animals and humans were also created a short time ago and have not undergone any major changes since their initial creation.
By 1860, one year after publication of the publication of The Origin of Species, there were four types of objection to the idea of evolution via natural selection.
1. It was scientifically wrong. 2. It was morally repugnant. 3. It was personally insulting. 4. It ran counter to a literal reading of biblical scripture
In the 140 years + since publication of Darwin's book On the Origin of Species (1859):
1. The scientific issues were settled rather quickly. Evolution as a fact - ancestry descent; new species arise from pre-existing ones. Evolution as a theory - natural selection as the principal mechanism.
2. Morally repugnant. A logical fallacy – why look to nature for moral guidance?
3. Personally insulting. Humans are part of nature, rather than apart from it. Get over it.
4. Counter to literal reading of the Bible. This is still with us, and is at the heart of what has come to be called "creationism". This motivation comes from a largely American sect of
Christianity commonly called "fundamentalism".
In the United States the strongest days of creationism were in the 1920s, when laws against the teaching of evolution were passed in Tennessee, Arkansas and Mississippi.
1925 Scopes trial in Dayton, TN. High school teacher John Scopes convicted of teaching evolution. Trial inhibited publishers of high school texts from including coverage of evolution.
1930's-present: The campaign against evolution in textbooks and curricula.
1960's - 1980's: The campaign for state laws mandating "equal time for creation-science and evolution-science"
1980's – present: Continuing pressure at the local and school board level. Textbook disclaimers (“Evolution is only a theory”), removing evolution from state science standards, adding “intelligent design” theory. Make evolution "controversial" and scare away its coverage.
"Biblical creationism" stresses the Biblical arguments against evolution.
"Scientific creationism” stresses evidence for a young earth, the absence of transitional fossils, and other arguments based on scientific grounds.
Institute for Creation Research (ICR), based in Santee, California (outside of San Diego). A
creationist think tank.
The basic content of "scientific creationism":
1. Special creation of universe and earth by a creator [e.g., not through natural processes] - God, Genesis.
2. Subsequent deterioration of earth and life. 2nd law of thermodynamics (entropy) causes things to "run down". The curse and the fall from grace in the Garden of Eden.
3. Special creation of life by a creator. God and the six days.
4. Fixity of "kinds" - no transitional forms between major groups. Small-scale evolution is OK, but birds from reptiles, whales from terrestrial mammals, not OK.
5. Distinct ancestry of humans and apes. God and Adam and Eve. Special creation.
6. Relatively recent origin of earth and life (somewhere between 6 and 10 thousand years)
7. Earth's geology a consequence of a worldwide flood and its aftermath. Noah's Flood, as in the Bible. The Grand Canyon as a example of the workings of “flood geology”
Some favorite creationist arguments:
1. Geological dating of rocks based on invalid assumptions.
2. Probability. amino acids, proteins, organs, life are much too complicated to have been form through chance.
3. 2nd law of thermodynamics makes evolution impossible. Evolution generates an increase in order, while the 2nd law states that in a closed (from the input of energy) system entropy (or disorder) increases though time.
4. No succession of appearance in the fossil record. Human footprints with dinosaur tracks, sandal prints with trilobites show that all kinds originated at the same time and co-existed. Any appearance of order is due to the Flood.
5. No evidence for human evolution. Australopithecines were apes. All of 'em.
6. No transitional forms. Archaeopteryx had feathers, it was 100% bird, not a transitional form with reptiles. Species to species transitions are just variations within kinds.
Until now, the creationist's efforts to get their doctrines and approaches into the public schools have been largely unsuccessful. Wherever state legislatures have passed laws giving creation science a place in the curriculum, these laws have been eventually ruled unconstitutional, based on the Bill of Rights' First Amendment calling for separation of church and state. The courts have recognized creationists as a group of people intent on pressing a particular religious viewpoint.
Fighting back: National Center for Science Education, Oakland, CA. Watches local and statewide schoolboards, provides support for high school teachers, press releases,
lobbies against creationist legislation, publishes bimonthly newsletter.