EVOLUTION UNIT 7A Part 1 of 2

EVOLUTION UNIT 7A

Part 1 of 2

DARWIN, NATURAL SELECTION, HARDY-

WEINBERG

Ch. 1 (p. 8-13) and Ch. 13 (all)

• All life is connected.• The basis for this kinship is

evolution• Evolution has transformed

life on Earth from its earliest beginnings to its extensive diversity today

• Evolutionary view came into focus in 1859 with Darwin’s book

• Photo on left is Charles Darwin (1809-1882)(British biologist) with son William in 1842.

• One of Britain’s most renowned biologists

• Published The Origin of Species 17 years later.

• Was the the most influential scientist in the development of modern biology.

• Buried next to Isaac Newton in London’s Westminster Abbey.

• 2 main points in book: • 1) species living today

descended from ancestral species = “descent with modification” = evolution

• Ex: the diversity of bears is based on different modifications of a common ancestor from which all bears descended.

• 2) the mechanism for evolution is “natural selection” (see next slides)

• Darwin loved nature. Disliked medical school. Became a minister. Became a naturalist for a voyage around the world when he was 22 years old.

• Darwin’s “Voyage of the HMS Beagle” is shown above.• Observed and collected thousands of specimens. Observed adaptations of

organisms. Most of animals of Galapagos Islands live nowhere else in world, but they resemble species living on the South American mainland. It was as though the animals strayed from mainland, then diversified as they adapted to environments on the different islands.

• Darwin saw large diversity of animals on

Galapagos Islands, off coast of South America

• If an ocean separated islands, it isolated 2 populations of a single species. The populations could diverge more and more in appearance as each adapted to local environmental conditions.

• After many generations, 2 populations could become dissimilar enough to be separate species - 14 species in the case of the birds called Galapagos finches. (This is now called divergent evolution)

• They have beak shapes and colorations that are adapted to their environments

• The beaks are adapted to certain food sources on the different islands; the colors protect them from predators

• See next page for the finches!

Darwin’s Finches

• Q:How did Darwin explain these adaptations, or different beaks?

• A:Natural selection! 3 main points:• 1. Far more offspring are produced than the

environment can hold. Overproduction leads to a struggle for existence among the individuals of a population.

• 2) Individuals in a population vary in many traits - no two individuals are alike.

• 3) Those individuals with traits best suited to the local environment will have the greatest reproductive success. They will leave the greatest number of surviving, fertile offspring. They will reproduce more of the same. This unequal reproductive success = natural selection.

• Nature decides what traits are most fit.• Adaptation is the accumulation of favorable

variations in a population over time. • Ex: beaks well equipped for available food

sources, and markings that reduce predation = finches survive to produce more. (Survival of the Fittest)

• Ex:(See diagram of natural selection in beetles)

•Darwin also looked at “Artificial Selection” going on with farming.•Humans have been modifying other species for centuries by selecting breeding stock with certain traits.•These vegetables and flowers no longer look like their ancestors.

Artificial Selection in pets - have been bred for human fancy.Dog breeds - all are descendants from one ancestral population of wolves“Humans” screened the heritable traits of populations instead of “nature’” or the natural environment.

• Natural selection in action today:

Antibiotic-resistant forms of tuberculosis-causing bacteria have made the disease a threat again in the U.S. The lung infection of this patient is shown in red.

• Example of human diversity.

• However, all humans are connected by descent from African ancestors.

• Example of natural selection - abuse of antibiotics has sped up the evolution of antibiotic-resistant bacteria.

• Evolution of

pesticide resistant insects: by spraying crops with poisons to kill insect pests, humans have favored the reproductive success of insects with inherent resistance to the poisons

• Related species of insects called mantids have diverse shapes and colors that evolved in different environments.

• Camouflage is an example of evolutionary adaptation.

A flower mantid in Malaysia

A leaf mantid in Costa Rica

• Evolution -2 modern definitions:

• A. the genetic compostion of a population changes over time

• B. all life descended from a common ancestor, from the earliest microbes to modern day organisms

• Darwin is ranked as the 4th most influential person of the past 1000 years. But who influenced him?

• Most scientists in Darwin’s day

thought:• Earth was young (6000 years old)• Earth was populated by millions of

unrelated species• Darwin’s book challenged that,

and was radical for its time• Anazimander (Greek philosopher)

had idea that life arose in water, and simpler forms of life preceded more complex ones.

• Aristotle (Greek philosopher)held that species are fixed or permanent, and do not evolve (are static).

Darwin, 1859

Darwin, 1874

• A cartoon of Charles Darwin - his book and beliefs were radical for its time

• Buffon (1700’s) (French naturalist) studied

fossils - said Earth may be much older than 6000 years. Proposed that a species in a fossil could be an ancient version of a living species

• Lamarck (1800’s) (French naturalist) said that life evolves through adaptation; ex: a powerful bird’s beak.

• However, he had an erroneous views of how adaptations evolve:

• He said “Inheritance of Acquired Characteristics” - by using or not using body parts, one can develop certain characteristics, which can pass on to offspring.

• Ex: if you exercise beaks and get stronger you can pass that trait down to offspring. (Use & Disuse Theory) Incompatible with modern genetics.

Lamarck

• Lyell (Scottish geologist) - said ancient

Earth was sculpted by gradual geologic processes that continue today. (Mountains, earthquakes, erosion.) Earth was very old. Gradualism principle.

• Wallace (British naturalist) (1850’s) developed a concept of natural selection identical to Darwin - both were presented to the scientific community.

• Darwin’s book evidenced 2 major points:

• Organisms on Earth today descended from ancestral species, accumulating different modifications or adaptations - “descent with modification.” History of life is analogous to a tree.

• Natural selection is the mechanism for descent with modification

Lyell

Wallace

Elephant family: Example of “descent with modification”

What is some evidence in support of evolution? (5

examples)

• 1. The Fossil Record

• Fossils - preserved remnants or

impressions left by organisms that lived in the past

• Most found in sedimentary rocks

• Younger strata are on top of older ones; positions of fossils in the strata reveal their relative age

• Fossil record - chronology of fossil appearances in rock layers, marking passing of geologic time

• Oldest fossils date from 3.5 billion years ago, are prokaryotes.

• Fishlike fossils are oldest vertebrates, then amphibians, reptiles, then mammals and birds.

• Paleontologists - scientists who study fossils - found fossilized whales that connect them to their land-dwelling ancestors

• 2. Biogeography- the geographic distribution of species

• Ex: Tropical animals in South America are more closely related to species in South American deserts than to species in African tropics.

• Ex: Australia has a diversity of pouched mammals (marsupials) but few placental mammals. They are hospitable to placental mammals. Unique Australian wildlife evolved on island continent in isolation from regions where early placental mammals diversified.

• Biogeography makes little sense if species were individually placed in suitable environments. Instead, species are where they are because they evolved from ancestors that inhabited those regions.

• Top photo shows the isolated Australian continent.

• Bottom photo shows pouched (marsupial) mammal; many marsupials are common to Australia.

• 3. Comparative Anatomy -

the same skeletal elements make up the forelimbs of humans, cats, whales, and bats - all are mammals.

• The functions differ, but structural similarity indicate they descended from a common ancestor -homology.

• Ex: forelimbs of diverse mammals, all have same bones (photo on left)

• Ex: human spine and knee joints derived from 4-legged mammals - are subject to sprains, spasms, common injuries because of our bipedal posture.

• Darwin Review:• 1. Overproduction of

offspring; competition for limited resources and struggle for existence

• 2. Individual variation• 3. Differential reproductive

success (natural selection). Environment (nature) determines who is fit. Those most fit survive & reproduce. Favored traits accumulate in population over generations = adaptive evolution.

1.Overproduction of spores

2.Variation in beetles

Ex: Vestigial Structures• These are some of the

most interesting homologous structures which have marginal, if any, use or importance to the organism. They are historical remnants of structures which had important functions in ancestors.

• Ex: the whales of today lack hind limbs, but have vestiges of pelvic and leg bones of their four-footed terrestrial ancestors.

• Vestigial organs are evidence of evolution - shows linkage to a past ancestor.

• 4. Comparative

Embryology - comparison of structures that appear during development of different organisms

• A sign that vertebrates evolved from a common ancestor: all of them have have an embryonic stage in which gill pouches appear on sides of throat

• At this stage, embryos of fish, frogs, snakes, birds & apes look more alike than different.

• As development progresses, the vertebrates take on more distinctive features.

• 5. Molecular Biology- there is a common genetic code shared by all species. This genetic language has been passed along through all branches of evolution since an early form of life.

• Ex: DNA bases same, RNA, amino acids, use ATP for energy.

• Ex: In above chart- chimps & humans are less than 2% different in DNA sequences

Natural Selection in Action• Ex: Evolution of finches on Galapagos Islands: the islands were colonized by finches that strayed from the South American mainland,then diversified on the different islands.Adaptive evolution/radiation.• Ex: Pesticides - do not create resistant individuals, but selects for resistant insects that were already present in the population

Large ground finch Woodpecker finch Small tree finch

• Ex: 2 populations of trees are separated by a river. (Partially isolated from each other)

• Trees are more likely to breed with members of the same population on same side of river.

• Could each side of trees evolve different traits?

• MODERN SYNTHESIS - the fusion of genetics with biology

• Study of variations in populations caused by mutations and sexual recombination

• Population-group of same species living in same area at same time.

• Looks at gene pools - all of the alleles in all the individuals making up a population

• Ex: Wildflower with only two varieties- Red flowers = R & white flowers = r.

• Suppose 80% or .8 of all flowers in the gene pool have the R allele.

• p = relative frequency of the dominant allele, so p = .8

• r must be present at the other 20%, or .2

• q = frequency of the recessive allele, so q = .2

• Since there are only 2 alleles for flower color, then p + q = 1

• If you know p, how can you find q? ________

• If you know q, how can you find p? ________

Variations (polymorphism) in garter snakes

• We have just found the

frequencies of alleles. (p + q = 1)• NEXT, we can find the

frequencies of the different genotypes in the population if the gene pool is completely stable (non-evolving).

• This is called Hardy-Weinberg equilibrium.

• G.H. Hardy, an English mathematician in 1908, and G. Weinberg, a German physician, asked “How can both dominant and recessive alleles remain in populations? Why don’t dominants simply drive out recessives? Ex: Brachydactylism is caused by a dominant allele, so why don’t most or all people have short, fat fingers?”

Hardy

• They found that genetic recombination does not by itself change the overall composition of the gene pool. To demonstrate this, they examined the behavior of alleles in an idealized population in which five conditions hold:

• 1. No mutations occur• 2. No net movement of individuals in or out of the

population• 3. Population is large enough• 4. Mating is random• 5. All alleles are equally viable (no natural selection)• (These are seldom likely to be met in a natural

population, but it provides a standard against which to measure.)

• This is Hardy-Weinberg equilibrium, or steady state.• Now, back to the problem...

• Back to the wildflower problem...

• p + q = 1

• .8 + .2 = 1

• Q: In the wildflower population, what is the probability of producing an RR individual by “drawing” two R alleles from the pool of gametes?

• R sperm x R egg, or p x p

• .8 x .8 = .64, or 64% of the plants in the population will have the RR genotype.

• Q: What is the frequency of rr individuals in the population?

• r x r, or q x q

• .2 x .2 = .04, or 4% of the plants in the population will have the rr genotype.

• Q: What is the frequency of Rr in the population?

• Rr + rR , or 2pq

• 2 (.8 x .2) = .32, or 32% are Rr with Red flowers.

• General formula = p2 + 2pq + q2 = 1

• You can also use a Punnett Square to do the same thing. (See left)

• How can we apply this to real life?

• Use the Hardy-Weinberg formula to calculate the percentage of a human population that carries the allele for a particular inherited disease: Ex: PKU.

• PKU occurs in about 1/10,000 babies born in U.S.

• If untreated, causes severe mental retardation; need a strict diet. It is a recessive genetic disease.

• Newborn babies are now routinely tested for PKU.

• A PKU baby is q2 = 1/10,000 = .0001.

• q = square root of .0001 or .01.

• p = 1 - q, or 1 - .01 = 0.99

• Carriers are 2pq or 2 x 0.99 x 0.01, or .0198.

• Thus,1.98% (around 2%) of the U.S. population carries the PKU allele. This is essential information for any public health program dealing with genetic diseases. (Note: Also do Punnett Square method on left.)

• Now-You try some problems in your UP. Remember: If they ask for frequency of an allele, that is p or q. If they ask for the % of individuals, that is pp or qq or 2pq. (The “individuals” are in the box.)

Do the Punnett Square here:

.0001

p q

p

q

• We just discussed a “non-evolving” population.

• How can we tell if a population is evolving?

• Ex: What if an insect is attracted to the white flowers instead of the red, and the white get pollinated more? This could cause the population to change over the generations.

• This is called microevolution, evolution on a small scale.

• 4 examples of microevolution:

• 1. Genetic Drift:

• 1. Genetic Drift - chance causes the frequencies of the alleles to change over the generations in a small gene pool, not natural selection. (The smaller the sample, the greater the chance of deviation from an idealized result.) See example above.

• 2 examples of Genetic Drift:• A. Bottleneck Effect - disasters

(earthquakes, floods, droughts, fires) may drastically reduce the size of a population.

• Small surviving population may not be representative of the original population’s gene pool.

• Some alleles may be lost from the gene pool - reducing the overall genetic variability in a population.

• Ex: Cheetahs have been overhunted. Only 3 small populations are left in wild; have low genetic variability. May be less adaptable to diseases, or environmental changes.

• B. The Founder Effect- a few

individuals colonize an isolated island, lake, or other new habitat

• The smaller the colony, the less its genetic makeup represents the gene pool of the original population from which they emigrated.

• Ex: In 1814, 15 people founded a British colony on small islands in Atlantic Ocean.

• One colonist carried a recessive allele for retinitis pigmentosa; causes blindness.

• In 1960’s, 4/120 descendants had it and 9 were carriers - much higher frequency than in Great Britain.

Tristan da Cunha. 1900’s

• Microevolution con’t.:

• 2. Gene Flow- a population may gain or lose alleles by genetic exchange with another population

• Ex: a windstorm blows pollen to our wildflowers from the neighboring white population - increases frequency of the white flower allele

• Tends to reduce genetic differences between population

A blend of several races: computer image. Are racesblending together due totravel and gene flow?

• 3. Mutations -change in organisms DNA.• Ex: a mutation causes white flowers to

produce red flowers.• Mutations at a particular gene locus are rare,

but the cumulative impact of all mutations at all loci can be significant.

• Over the long term, mutation is important to evolution - it serves as the raw material for natural selection.

• 4. Natural Selection - a blend of chance and sorting.

• Those that work best in the environment leave the most offspring, and have a disproportionate impact on the gene pool.

• Darwinian fitness - the contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals

• Ex: (left) Flowers which attract the most pollinators are most fit

• 3 outcomes of natural selection:

• 1) Directional selection - selects in favor of some extreme phenotype, when environment changes. Ex: pesticide resistant individuals

• 2) Diversifying selection - leads to a balance between 2 or more contrasting morphs. Ex: a patchy environment with snakes

• 3) Stabilizing selection - maintains variation for a trait within a narrow range.. Ex: majority of human birth weights 6.5-9 pounds. Occurs in a relatively stable environment, populations are already well adapted.

End Thought: Population Genetics of Sickle-Cell Allele

• Why is the sickle-cell allele so much more common in African Americans than in the general U.S. population?

• In some African populations, sickle-cell allele has a frequency of 0.2, or 20%.

• This is q. • Q: Find the number of individuals that

benefit from having a sickle cell allele, (resistant to malaria) vs. how many get the disease from it. (Do a punnett square.)

• A: 32% benefit, 4% get the disease• This explains the high frequency of

the sickle cell allele compared to other disease alleles.

• This is “Darwinian medicine” - Biology is the foundation of all medicine.

UNIT 7B:

EVOLUTION & HUMAN ANCESTRY

Ch. 15, 14, and 17

HONORS BIOLOGY

• Examine the

chart on the left.

• What are some major episodes in the history of life?

• Q: What is this chart based on?

• A: Fossil evidence and molecular analysis.

How did life on ancient Earth evolve? (Ch. 15)

Conditions on Early Earth:

• 1. Q: When was Planet Earth born?

• A: About 4.5 billion years ago.

• How? A current belief is “The Big Bang” theory:

• 10-20 billion years ago the universe was a dense compaction that exploded, hurling dust, debris, & gases into space.

• Material has been hurling outward ever since; universe is still expanding.

• Materials cooled, atoms like H and He formed. Cooling and compression formed stars & planets. Our sun formed 5-10 billion years ago. Material ejected from sun formed planets.

• Earth was originally cold, but heat built up with gravitational compaction, radioactive decay, gases and heat from hot springs and volcanoes, or a collision with other objects.

• 2. What was the early atmosphere like

on earth?

• CO2, H2O, CO, H2, N2, HN3 (ammonia), H2S and CH4 (methane).

• No free O2 present.

• Earth slowly cooled, water vapor condensed, rains fell forming oceans. Erosion from earth’s surface added minerals, making them “salty.”

• 4 conditions were necessary for chemical evolution to occur:

• 1. Absence of free O2 (it would have broken down organic molecules)

• 2. Energy (violent storms, volcanoes, UV radiation)

• 3. Chemicals

• 4. Time

• Geologic evidence shows appearance of simple life forms 3.5 billion years ago.

• 3. How did Organic Molecules

form?

• Oparin hypothesis, later tested by Urey and Miller, 1950’s

• Designed an apparatus that simulated conditions on early earth.

• Started with H2, CH4, H2O, and NH3.

• Exposed it to an electric discharge, simulated lightning.

• Produced amino acids and other building blocks!

• Similar experiments involving different combinations of gases have produced produced a variety of organic molecules including RNA and DNA bases.

Stanley Miller

• 4. How did life form?

• The ancient Greeks believed in “spontaneous generation,” life from non-living things.

• In 1862, Louis Pasteur, using bacteria, proved “life-from-life,” or biogenesis.

• How did first life on Earth form?

• Hypothesis is: Earth’s primordial environment (organic soup) could eventually have produced very simple cells through a sequence of stages.

• See next slide for stages:

Louis Pasteur

Earth 3 billion years ago.(drawing). Pads are colonies of prokaryotes

• 4-Stage Hypothesis for the Origin of Life:

• Stage 1: Synthesis of small organic molecules from abiotic chemicals. (Stanley Miller experiment. Others have produced all 20 A.A., sugars, lipids, ATP, and monomers of DNA & RNA). OR - organic compounds could have reached the Earth from space.

• Stage 2: Link above organic monomers together to form polymers. (Have formed polypeptides by dripping monomers onto hot sand, clay or rock.)

• Stage 3: Origin of Self-Replicating Molecules, like RNA, for inheritance.(Short strands of RNA can assemble spontaneously from nucleotide monomers.) (See above picture.)

• Stage 4: Formation of Pre-Cells -

molecular packages with some of the properties of life (see left) (Laboratory experiments demonstrate this.)

• With natural selection and evolution these pre-cells could become more cell-like.

• Prokaryotes flourished at least 3.5 billion years ago; Bacteria was unicellular, anaerobic, asexual, heterotrophic.

• With chlorophyll, bacteria became photosynthetic/autotrophic, O2 was introduced into atmosphere, ozone layer formed.

• With time; aerobic organisms, eukaryotic cells, sexual reproduction, multicellular organisms.

• END OF CH. 15 NOTES

The pre-cell

How Do Species on Earth Evolve? (Ch. 14)

• The history of life on Earth includes stories of species dying out while other multiply and diversify.

• How are new species made?

• How do species die off?

• Ex: All dinosaurs, and 1/2 of other species at the time, became extinct in less than 10 million years. Why?

• Fossil record shows that climate cooled, shallow seas receded, & a large meteorite or asteroid hit Earth which blocked light, disturbed climate, killed off many plant species. Why did plant-eating dinosaurs die out first?

Huge impact crater when ameteorite or asteroid slammedinto Earth, in Caribbean Sea.

• Q: How does macroevolution

occur? Macroevolution = multiplication of species, biological diversity, evolutionary novelty (wings, feathers, big brains)

• A: The beginning of new forms of life can occur through speciation - the origin of new/different species.

• Ex: See Left

• Nonbranching - a population changes through adaptation to a changing environment. Becomes a new species.

• Branching - one or more new species branch from a parent species that may continue to exist.

• Species - a population(s) whose

members have the potential to interbreed with one another in nature to produce fertile offspring, and cannot with members of other species.

• Ex: (Left) These birds look similar, but cannot interbreed with one another. Q: Are they two different species?

• Yes.

• Ex: Breeds of dogs look different from one another, but all can interbreed. Q: Are they all different species?

• No. They are all the same species.

• Ex: These humans may live in

different geographical areas, and may never get together. But if they did, could they interbreed? Are they the same species?

• Yes, all humans belong to the same species.

• Q: Are humans and chimpanzees the same species?

• A: No• Q: What about dogs and

wolves?• A: No.

Q: What prevents two species from reproducing with each other?A: Reproductive Barriers!

• 2 types of Reproductive Barriers:

• I. Pre-zygotic barriers - impedes mating or hinders fertilization of eggs.

• A. Temporal isolation - time based. Ex: Western spotted skunks breed in the fall, but eastern species breed in late winter.

• B. Habitat isolation - spatially segregated. Ex: one species of garter snake lives in water, and a closely related species lives on land.

• C. Behavioral isolation - courtship rituals. Ex: in bird species, courtship is so elaborate that individuals are unlikely to mistake a bird of a different species as one of their kind.

Courtship rituals of Blue-footed boobies in Galapagos Islands. Male does “high-step,”showing bright blue feet.

• D. Mechanical isolation -

male and female sex organs of different species are anatomically incompatible. Ex: 2 insects’ copulatory organs may not fit together correctly; no sperm is transferred.

• E. Gametic isolation - individuals may copulate, but their gametes are incompatible and fertilization does not occur. Ex: mammal sperm may not survive in female of a different species.

Horse + Donkey = Mule(but is sterile)

II. Post-zygotic barriers - if mating actually occurs between different species and a zygote is formed, these mechanisms affect the hybrid offspring. (baby) A. Hybrid inviability - the hybrid offspring die before reaching reproductive maturity. Ex: certain frogs B. Hybrid sterility - the hybrid offspring may become vigorous adults, but are infertile. Ex: see below

Some confusing hybrids…By far the largest and most unusual cat at the Shambala Preserve, Patrick is a liger: the hybrid offspring of a lion father and a tiger mother. Weighing in at an estimated800 pounds, his ruddy coat shows faint stripes and he also has a modest mane. He "fuffs" like a tiger and roars like a lion, although without adding the deep grunts at the end that most lions do. www.shambala.org

Patrick,a liger

A wolf hybrid

Noelle, on right is a tigon (tiger fatherand lioness mother, born in 1978) She was thought to be sterile, but aftermating with a male Siberian tiger, shegave birth to Nathaniel on left in1983, a ti-tigon. Both have since died.

• Mechanisms of Speciation:

• When the gene pool of a population is separated from other parent species populations, then the new population can follow its own evolutionary course. 2 Types:

• 1. Allopatric speciation - (“other country”) - a physical barrier physically isolates the new population. (see left)

• Ex: mountain range, glaciers, bridges, lakes, islands, canyons

• More likely when a population is small & isolated

• 2. Sympatric speciation - (“together country”) - the new population becomes reproductively isolated right in the midst of the parent population. (see left)

• Ex: 25% of all plants, incld. wheat

• Plants have accidents during cell division, become polyploid cells - each cell has more than 2 complete sets of chromosomes. Can no longer mate w. parent population.

• All squirrels used to be the same in the Grand Canyon. Over time, one population migrated to the south rim (left), the other to the north rim (right). Due to the large distance, the 2 populations seldom got back together. Each population adapted differently to their surroundings, had different mutations. Now they cannot mate and produce fertile offspring.

• Q: Are they the same or different species?

• Q: What is this an example of?

• A: Different species; Allopatric speciation

Explain this diagram:

•

• How fast can speciation occur?

• Gradualist model - traditional evolutionary trees show branches diverge gradually

• Punctuated equilibrium model - more recent - species diverge in spurts of relatively rapid changes, instead of slowly and gradually.

• Ex: polyploidy is sudden speciation

• Ex: a species has a spurt of evolution its first 50,000 years, then has little or no change for 4 million years, then becomes extinct.

The Evolution of Biological Novelty

• How can we account for flight in birds?

• Birds are derived from earthbound reptiles.

• Birds have lightweight skeletons w. honeycombed bones, homologous to reptilian ancestors.

• These bones/winglike forelimbs must have had some function on the ground.

• The first flights may have only been glides/hops.

• Natural selection - those who were able to fly better, survived.

The Fossil Record• The fossil record is an archive of

macroevolution.

• A 40 million year old leaf in sedimentary rock. (top left)

• A fossilized dinosaur bone in sandstone in Dinosaur National Park in Utah and Colorado. (top right)

• Petrified stone trees in Petrified National Forest in Arizona are about 190 million years old.

• A 30 million year old scorpion embedded in amber. (hardened resin from a tree).

Fossils Continued

• The skull of Homo erectus, an ancestor of humans that lived about 1.5 million years ago. (top left)

• These casts form when the shells of decayed marine organisms called ammonites are filled by minerals dissolved in water. (top right)

• Trace fossils are foot prints, burrows, and other remnants of ancient organism’s behavior.(bottom left)

• These tusks belong to a whole 23,000 year old mammoth, which scientists discovered in Siberian ice in 1999. (bottom right)

How can we tell geologic time using fossils?

• Fossil record shows macroevolution.

• Sedimentary rocks are richest sources of fossils

• Provide a record of life on Earth in their layers

• Dead organisms get trapped in sediments, freezing fossils in time

• Younger sediments are superimposed on older ones; layers of sediment tell the relative ages of fossils.

• A Geologic time scale can be made, studying many different sites

• Geologists divided time into 4 eras: Precambrian, Paleozoic, Mesozoic, & Cenozoic (see packet charts & text p. 283)

• Can tell relative ages of fossils - older fossils are in the lowest layers.

Dinosaur bone

• For absolute dating, scientists use radiometric dating to determine the ages of fossils in years.

• Scientists measure the radiation that fossils emit as they decompose. This clock-like decay can be used to date fossils.

• Ex: Carbon-14 is found in organisms and is radioactive. It takes 5600 years for half of the C14 to decay after an organism dies; that is its half-life.

• The age of a fossil is determined by measuring the ratio of C14 relative to the more common C12. (The less C14, the older the fossil.)

• Ex: If ratio of C14 to C12 is 25% that of a living organism, that means it went through 2 half-lives. 5600 x 2 = 11,200 years old. (see chart)

• Because the half-life of carbon-14 is relatively short,

the isotope is only useful for

dating fossils less than about

50,000 years old. To date older fossils, paleontologists use radioactive isotopes with longer half-lives.

• Plate boundaries

• San Andreas Fault in California - many earthquakes occur at plate boundaries. This fault is at the border where 2 plates slide past each other.

Evolution and Geology:

• The history life has included

many extinctions.

• Extinction of a species may occur because its habitat has been destroyed, or unfavorable climatic changes.

• 6 distinct periods of mass extinction over the last 600 million years.

• The rate of species loss world-wide may be 50 times higher now than at any time in the past 100,000 years. Why?

• See video “Extinction”

• END OF CH. 14 NOTESThe extinct Dodo bird

• Continental Drift:

• Continents used to be locked up-Pangaea

• Later drifted apart,and began to break up

• Reshaped biological diversity-caused extinctions, and new opportunities for survivors.

• One result: Isolated continent of Australia - fauna and flora contrast sharply with rest of the world.

• Humans emerged on

one very young twig on the vertebrate branch.

• Humans and chimps diverged from a common ancestor 5-7 million years ago.

• Q: Are our ancestors chimps or modern apes?

• A: No. We represent 2 divergent branches of the anthropoid tree that evolved from a common ancestor.

• Chimps are more like our cousins or siblings, but not our parent species.