MODULE 2: Slide Set 1MODULE 2: Slide Set 1

Chapter 15Chapter 15Origin of Life, Eukaryotes and MulticellularityOrigin of Life, Eukaryotes and Multicellularity

Read Ch 15 and do the activities at “Mastering Biology”Read Ch 15 and do the activities at “Mastering Biology”

Chapter 15Chapter 15 Life’s Origin and Early HistoryLife’s Origin and Early History Spontaneous GenerationSpontaneous Generation AbiogenesisAbiogenesis

Oparin/Haldane: “chemical evolution hypothesis”Oparin/Haldane: “chemical evolution hypothesis” Stanley Miller: Abiotic synthesis…Stanley Miller: Abiotic synthesis…

BiogenesisBiogenesis Early stagesEarly stages Lynn Margulis: Endosymbiosis Lynn Margulis: Endosymbiosis Origin of Multi-celled organismsOrigin of Multi-celled organisms

The 4 Paradigms of Modern BiologyThe 4 Paradigms of Modern Biology(you could actually make this 3)(you could actually make this 3)

1. Evolutionary Theory1. Evolutionary Theory

2. Cell Theory2. Cell Theory

3a. 3a. Biology obeys the laws of physics and chemistry for Biology obeys the laws of physics and chemistry for mattermatter

3b. 3b. Biology obeys the laws of physics and chemistry for Biology obeys the laws of physics and chemistry for energyenergy

in vivo in vivo vs. vs. in vitroin vitro

Biology and Society: Biology and Society: Can Life Be Created in the Lab?Can Life Be Created in the Lab?

How did life first arise on Earth?How did life first arise on Earth? To gain insight, scientists have recently To gain insight, scientists have recently (2010)(2010)

• Synthesized the entire genome of Synthesized the entire genome of Mycoplasma Mycoplasma genitalium, genitalium, a species of bacteria found naturally in the a species of bacteria found naturally in the human urinary tracthuman urinary tract

• Transplanted the complete genome of one species of Transplanted the complete genome of one species of Mycoplasma Mycoplasma bacteria into anotherbacteria into another

© 2010 Pearson Education, Inc.

Figure 15.00

MAJOR EPISODES IN THE HISTORY OF MAJOR EPISODES IN THE HISTORY OF LIFELIFE

Earth was formed about 4.6 billion years ago. Earth was formed about 4.6 billion years ago. ProkaryotesProkaryotes

• Evolved by 3.5 billion years agoEvolved by 3.5 billion years ago

• Began oxygen production about 2.7 billion years agoBegan oxygen production about 2.7 billion years ago

• Lived alone for almost 2 billion yearsLived alone for almost 2 billion years

• Continue in great abundance todayContinue in great abundance today Single-celled Single-celled eukaryoteseukaryotes first evolved about 2.1 billion first evolved about 2.1 billion

years ago.years ago. Multicellular eukaryotes first evolved at least 1.2 billion years Multicellular eukaryotes first evolved at least 1.2 billion years

ago.ago.

Major episodes in History of LifeMajor episodes in History of Life

Precambrian

Common ancestor to

all present-day life

Origin of

Earth Earth cool enough

for crust to solidify Oldest prokaryotic fossils

Atmospheric oxygen

begins to appear due

to photosynthetic

prokaryotes

Millions of years ago

4,5004,000 3,500 3,000 2,500

Figure 15.1a

Paleozoic Mesozoic Cenozoic

Bacteria

Archaea

Plants

Fungi

Animals

Pro

karyotes

Eu

karyotes

Pro

tists

Oldest eukaryotic

fossils

Origin of

multicellular

organisms

Oldest

anim

al

fossils

Plants and

symbiotic fungi

colonize land

Extinction of

dinosaurs

First humans

Millions of years ago

Cambrian

explosion

2,000 1,500 1,000 500 0

Figure 15.1b

Precambrian

All the major phyla of animals evolved by the end of All the major phyla of animals evolved by the end of the Cambrian explosion, which began about 540 the Cambrian explosion, which began about 540 million years ago and lasted about 10 million years.million years ago and lasted about 10 million years.

Plants and fungi Plants and fungi • First colonized land about 500 million years First colonized land about 500 million years • Were followed by amphibians that evolved from fishWere followed by amphibians that evolved from fish

What if we use a clock analogy to tick down all of the What if we use a clock analogy to tick down all of the major events in the history of life on Earth?major events in the history of life on Earth?

Origin of Life: first prokaryotes ~3.5 byp

Photosynthesis and atmospheric oxygen appear ~2.7 byp

Single-celled eukaryotes ~2.1byp

Multicellular eukaryotes ~ 1.2 byp

Animals ~0.54 byp

Colonization of land ~0.5 byp

Homo habilis ~ 0.0024 byp

THE ORIGIN OF LIFETHE ORIGIN OF LIFE We may never know for sure how life on Earth began.We may never know for sure how life on Earth began.

Resolving the Biogenesis ParadoxResolving the Biogenesis Paradox All life today arises by the reproduction of preexisting life, or All life today arises by the reproduction of preexisting life, or

biogenesisbiogenesis.. If this is true, how could the first organisms arise?If this is true, how could the first organisms arise? From the time of the ancient Greeks until well into the 19From the time of the ancient Greeks until well into the 19 thth

century, it was commonly believed that life regularly arises from century, it was commonly believed that life regularly arises from nonliving matter, an idea called nonliving matter, an idea called spontaneous generationspontaneous generation..

spontaneous generation spontaneous generation vs vs abiogenesis abiogenesis vsvs biogenesis biogenesis

The 4 Paradigms of Modern BiologyThe 4 Paradigms of Modern Biology(you could actually make this 3)(you could actually make this 3)

1. Evolutionary Theory1. Evolutionary Theory

2. Cell Theory2. Cell Theory

3a. 3a. Biology obeys the laws of physics and chemistry for Biology obeys the laws of physics and chemistry for mattermatter

3b. 3b. Biology obeys the laws of physics and chemistry for Biology obeys the laws of physics and chemistry for energyenergy

in vivo in vivo vs. vs. in vitroin vitro

vitalists vs mechanistsvitalists vs mechanists(mechanists become reductionists)(mechanists become reductionists)

..

Reductionists say: the processes of life can be Reductionists say: the processes of life can be explained by the laws of physics and chemistry.explained by the laws of physics and chemistry.

in vivo in vivo (in life)(in life) in vitro in vitro (in “glass”)(in “glass”)

““Spontaneous Generation”Spontaneous Generation”

The idea that life can arise spontaneously The idea that life can arise spontaneously from non-living things.from non-living things.

Francisco RediFrancisco Redi

Needham, Spallanzani, PasteurNeedham, Spallanzani, Pasteur

Life DOES NOT arise spontaneouslyLife DOES NOT arise spontaneously Pasteur: “Never will the concept of spontaneous generation recover Pasteur: “Never will the concept of spontaneous generation recover

from the mortal blow of my simple experiments.”from the mortal blow of my simple experiments.”

A.I. Oparin and J.B.S. HaldaneA.I. Oparin and J.B.S. HaldaneBiogenesisBiogenesis

The Idea of Chemical Evolution

Freidrich Wöhler, Freidrich Wöhler, 18281828

"I cannot, so to say, hold my chemical water and must tell you that I can

make urea without thereby needing to have kidneys, or anyhow, an

animal, be it human or dog".

FermentationFermentationHans und EduardHans und Eduard

BuchnerBuchner

to vacuum pump

CH4

NH3

H2OH2

gases

electrodes

spark discharge

water out

condenser

water in

water droplets

water containingorganic compounds

liquid water in trapboiling water

Fig. 20-4c, p.321

First First AtmosphereAtmosphere

““Ur-atmosphere”Ur-atmosphere”

NO OXYGENNO OXYGENNO OXYGENNO OXYGENNO OXYGENNO OXYGEN

An iconicAn iconicexperiment.experiment.

We have We have alternate revised alternate revised

hypotheses hypotheses today.today.

Jeffrey Bada, Nazi Syn-fuelsJeffrey Bada, Nazi Syn-fuelsS.M. 1953. 5 AA’s; J.B. 2008, 22 AA’sS.M. 1953. 5 AA’s; J.B. 2008, 22 AA’s

•So… life arises on the primitive Earth quickly... 400 So… life arises on the primitive Earth quickly... 400 million years at most.million years at most.

Earth is anaerobic, NO OXYGEN.Earth is anaerobic, NO OXYGEN.

Life is entirely prokaryotic in the beginning.Life is entirely prokaryotic in the beginning.

Prokaryotes dominate for half of life’s history; in truth, Prokaryotes dominate for half of life’s history; in truth, they dominate today.they dominate today.

But we also have the Eukarya today. Where did they But we also have the Eukarya today. Where did they come from???come from???

We need evolution of eukaryotes AND we need We need evolution of eukaryotes AND we need evolution of multicellularity.evolution of multicellularity.

We’ll come back to that. First a survey of Life… We’ll come back to that. First a survey of Life…

What are the kinds of life?What are the kinds of life?

What are the kinds of living “things” we find What are the kinds of living “things” we find on our planet???on our planet???

There are lots of useful ways There are lots of useful ways to classify lifeto classify life

Phylogenetic ClassificationPhylogenetic Classification

Ecological ClassificationEcological ClassificationSpatial/Lifestyle ClassificationSpatial/Lifestyle Classification

Phylogenetic classification is based Phylogenetic classification is based on evolutionary relationships.on evolutionary relationships.

PHYLOGENETIC CLASSIFICATIONPHYLOGENETIC CLASSIFICATION

Phylogenetic classification is classification Phylogenetic classification is classification based on phylogeny, i.e. evolutionary based on phylogeny, i.e. evolutionary relationships.relationships.

Organisms are placed in a group because, Organisms are placed in a group because, as best we can tell, they are related as best we can tell, they are related evolutionarily. evolutionarily.

So phylogenetic classification puts bats So phylogenetic classification puts bats and whales in the same group (Mammals) and whales in the same group (Mammals) and in a different group than fish or birds.and in a different group than fish or birds.

The Three DomainsThe Three DomainsPHYLOGENETIC CLASSIFICATION PHYLOGENETIC CLASSIFICATION

Who’s related to whom?Who’s related to whom?

Biology’s gigantic Maury Povich ShowBiology’s gigantic Maury Povich Show

The 3 Domains, Carl WoeseThe 3 Domains, Carl Woese1967, 19901967, 1990

Domains are the largest taxa !Domains are the largest taxa !There are 3 domains. These are based in There are 3 domains. These are based in

similarities and differences in ribosomal RNA.similarities and differences in ribosomal RNA.

Origin of life

Eubacteria

Archaebacteria

Eukaryotes

Protistans

Plants

Fungi

Animals

The Domains are sometimes The Domains are sometimes divided into 6 Kingdomsdivided into 6 Kingdoms

Phylogenetic ClassificationPhylogenetic Classification(based on phylogeny, i.e. evolutionary relationships)(based on phylogeny, i.e. evolutionary relationships)

The 3 Domain System is replacing The 3 Domain System is replacing the 6 Kingdom system.the 6 Kingdom system.

(But who cares if the big shots are (But who cares if the big shots are “rearranging the furniture” upstairs?) “rearranging the furniture” upstairs?)

We will be using the 6 kingdom We will be using the 6 kingdom system for ease of communication system for ease of communication

and to get us to the (lowly?) and to get us to the (lowly?) animals… the things this course is animals… the things this course is

supposed to be about. supposed to be about.

energy input, from sun

NutrientCycling

Prodcers(plants, and other self-

feeding organisms)

ConsumersAnimals, most fungi, many

protists, many bacteria

energy output (mainly metabolic heat)

Fig. 1-3, p.6

What are the kinds of living things on Earth?What are the kinds of living things on Earth?ECOLOGICAL CLASSIFICATIONECOLOGICAL CLASSIFICATION

Ecological ClassificationEcological ClassificationBased on organism’s role in the ecosystemBased on organism’s role in the ecosystem

AUTOTROPHS (Producers or Primary Producers)AUTOTROPHS (Producers or Primary Producers) HETEROTROPHSHETEROTROPHS

Consumers Consumers DecomposersDecomposers

Autotrophs and HeterotrophsAutotrophs and Heterotrophs

Producers, Consumers, DecomposersProducers, Consumers, Decomposers

H2O + CO2C6H12O6 + O2

Water + Carbon Dioxide Glucose +

p.111

light energy

enzymes

EnergeticsEnergeticsautotrophic vs. heterotrophicautotrophic vs. heterotrophic

Oxygen

C6H12O6 + O2

PHOTOSYNTHESISPHOTOSYNTHESIS

RESPIRATIONRESPIRATION

Glucose + Oxygen

H2O + CO2

Water + Carbon Dioxide

Systems of ClassificationSystems of Classification ““Spatial”/”Lifestyle” Classification Spatial”/”Lifestyle” Classification

PlanktonPlankton NektonNekton BenthosBenthos

Kingdom

Animalia

Domain Archaea

Earliest

life

Domain Bacteria

Domain Eukarya

Kingdom

Fungi

Kingdom

Plantae

The protists

(multiple kingdoms)

Figure 14.25

We will concentrate on the 6 kingdoms !We will concentrate on the 6 kingdoms !So…So…

How do we distinguish among the six kingdoms?How do we distinguish among the six kingdoms?

Cell NumberCell Number unicellular vs. multicellularunicellular vs. multicellular

Cell TypeCell Type prokaryotic vs. eukaryoticprokaryotic vs. eukaryotic

EnergeticsEnergetics autotrophic vs. heterotrophicautotrophic vs. heterotrophic

Cell NumberCell Numberunicellular vs. multicellularunicellular vs. multicellular

Cell TypeCell Typeprokaryotic vs. eukaryotic cellsprokaryotic vs. eukaryotic cells

Cell TypeCell Typeprokaryotic vs. eukaryotic cellsprokaryotic vs. eukaryotic cells

karyon gk. “kernel of corn”karyon gk. “kernel of corn” Prokaryotic cells are:Prokaryotic cells are:

Simpler, smaller, less specialized, less compartmentalized.Simpler, smaller, less specialized, less compartmentalized. Most-notably, they lack a nucleus (and mitochondria, etc.)Most-notably, they lack a nucleus (and mitochondria, etc.) Bacteria (=Eubacteria), Archaea (=Archaebacteria)Bacteria (=Eubacteria), Archaea (=Archaebacteria)

Eukaryotic cells are:Eukaryotic cells are: More complex, more specialized, compartmentalizedMore complex, more specialized, compartmentalized They have a well-defined nucleus (and mitochondria, etc.)They have a well-defined nucleus (and mitochondria, etc.) Domain EukaryaDomain Eukarya

• Protista, Fungi, Plantae AnimaliaProtista, Fungi, Plantae Animalia

EnergeticsEnergeticsautotrophic vs. heterotrophicautotrophic vs. heterotrophic

Autotrophs produce their own foodAutotrophs produce their own food Photosynthesis, chemosynthesisPhotosynthesis, chemosynthesis Also called producers or primary producersAlso called producers or primary producers Some bacteria, some protists, “all” plantsSome bacteria, some protists, “all” plants

Heterotrophs do not make foodHeterotrophs do not make food They have to eat some other organismThey have to eat some other organism Consumers and decomposersConsumers and decomposers Some bacteria, some protists, animals, fungiSome bacteria, some protists, animals, fungi

H2O + CO2C6H12O6 + O2

Water + Carbon Dioxide Glucose +

p.111

light energy

enzymes

EnergeticsEnergeticsautotrophic vs. heterotrophicautotrophic vs. heterotrophic

Oxygen

C6H12O6 + O2

PHOTOSYNTHESISPHOTOSYNTHESIS

RESPIRATIONRESPIRATION

Glucose + Oxygen

H2O + CO2

Water + Carbon Dioxide

C’s and H’s and O’sC’s and H’s and O’srearrange to makerearrange to make

C’s and H’s and O’s C’s and H’s and O’s!!!!!!

Carbon dioxide and Water make Sugar and OxygenCarbon dioxide and Water make Sugar and Oxygen and then… and then…

Sugar and Oxygen make Carbon dioxide and Water.Sugar and Oxygen make Carbon dioxide and Water.and then…and then…

Carbon dioxide and Water make Sugar and OxygenCarbon dioxide and Water make Sugar and Oxygenand then…and then…

Sugar and Oxygen make Carbon dioxide and WaterSugar and Oxygen make Carbon dioxide and Water

So, what’s up with that?So, what’s up with that?

It’s all about the It’s all about the BigBig EEBiggie, R.I.P. How does he do that? Biggie, R.I.P. How does he do that?

What fuels him?What fuels him?

THE SIX KINGDOMS OF LIFETHE SIX KINGDOMS OF LIFEKINGDOMKINGDOM UNIUNI / / MULTIMULTI PROPRO / / EUEU AUTO AUTO / / HETEROHETERO

BACTERIABACTERIA

ARCHAEAARCHAEA

PROTISTAPROTISTA

FUNGIFUNGI

PLANTAEPLANTAE

ANIMALIAANIMALIA

THE SIX KINGDOMS OF LIFETHE SIX KINGDOMS OF LIFEKINGDOMKINGDOM UNIUNI / / MULTIMULTI PROPRO / / EUEU AUTO AUTO / / HETEROHETERO

BACTERIABACTERIA UNIUNI PROPRO A / HA / H

ARCHAEAARCHAEA UNIUNI PROPRO A / HA / H

PROTISTAPROTISTA UNI / MULTIUNI / MULTI EUEU A / HA / H

FUNGIFUNGI UNI / MULTIUNI / MULTI EUEU HH

PLANTAEPLANTAE MULTIMULTI EUEU AA

ANIMALIAANIMALIA MULTIMULTI EUEU HH

EUBACTERIAEUBACTERIAthe “true” bacteriathe “true” bacteria

ArchaeaArchaea, , the “extremophiles”the “extremophiles”methanogens, thermophiles, halophilesmethanogens, thermophiles, halophiles

THE PROTISTATHE PROTISTAa polyphyletic kingdom, “fer shure”a polyphyletic kingdom, “fer shure”

KINGDOM FUNGIKINGDOM FUNGImushrooms, mold mildew, yeastsmushrooms, mold mildew, yeasts

heterotrophic uni / multi, eukaryotesheterotrophic uni / multi, eukaryotes

KINGDOM PLANTAEKINGDOM PLANTAEautotrophic, multicellular, eukaryotesautotrophic, multicellular, eukaryotes

Fig. 1-8c(10), p.9

KINGDOM ANIMALIAKINGDOM ANIMALIAHeterotrophic, multicellular, eukaryotesHeterotrophic, multicellular, eukaryotes

Fig. 19-19, p.314

livingcells

formation ofprotein-RNA systems,

evolution of DNA

formation oflipid spheres

spontaneous formation of lipids,carbohydrates, amino acids, proteins,nucleotides under abiotic conditions

membrane-bound proto-cells

self-replicating system enclosed in aselectively permeable, protective lipid sphere

DNA RNA enzymes andother proteins

Stepped Art

Fig. 20-7c, p.323

Archaean Eon: 3.8-2.5 BYPArchaean Eon: 3.8-2.5 BYP

Fig. 20-7, p.324

The Golden Age of ProkaryotesThe Golden Age of Prokaryotes

Rise of EukaryotesRise of EukaryotesThe Oxygen RevolutionThe Oxygen Revolution

About 2.5 BYP PHOTOSYNTHESIS !About 2.5 BYP PHOTOSYNTHESIS ! The Oxygen Revolution had 2 irreversible The Oxygen Revolution had 2 irreversible

effects:effects: Abiogenesis shut down by oxygen !Abiogenesis shut down by oxygen ! Aerobic Respiration evolves and makes Aerobic Respiration evolves and makes

“getting energy” from food much more “getting energy” from food much more efficient !!efficient !!

Fig. 20-7, p.324

Theory of EndosymbiosisTheory of Endosymbiosis Lynn Margulis (our old friend from week 2) says…Lynn Margulis (our old friend from week 2) says… Mitochondria and chloroplasts are the descendents of free-Mitochondria and chloroplasts are the descendents of free-

living prokaryotic organisms living prokaryotic organisms Prokaryotes were engulfed by early eukaryotes and became Prokaryotes were engulfed by early eukaryotes and became

permanent internal symbionts. permanent internal symbionts. Oh yeah sure! This one eats that one and that one eats this one Oh yeah sure! This one eats that one and that one eats this one

and then this one becomes a part of that one and then you got, and then this one becomes a part of that one and then you got, like, you know, people??? like, you know, people???

You have some evidence for that? You have some evidence for that? Well, I’m glad you asked.Well, I’m glad you asked.

Zooxanthellae, Zoochlorellae, ZoocyanellaeZooxanthellae, Zoochlorellae, Zoocyanellaesymbiotic algae living inside various animals is symbiotic algae living inside various animals is commoncommon in biology in biology

Mitochondrial DNAMitochondrial DNAChloroplast DNAChloroplast DNA

Bacterial DNABacterial DNA

hydrogen-rich anaerobic atmosphere atmospheric oxygen, 10%

archaean lineage

dancestors ofeukaryotes

hendomembrane

system and nucleus

b

origin ofprokaryotes

cyclic pathwayof photosynthesis

e

noncyclic pathwayof photosynthesisf

g aerobic respiration

3.8 billion years ago

3.2 billion years ago

2.5 billion years ago

a

Fig. 20-12a, p.328

Fig. 20-12b, p.328

atmospheric oxygen, 20%; the ozone layer slowly develops

iendosymbiotic

origin of mitochondira

jorigin of eukaryotes,

the first protists

k origin of animals

jendosymbiotic origin

of chloroplasts

Aerobic species becomes endosymbiot of anaerobic forerunner of eukaryotes.

k origin of fungi

k origin of lineage leading to plants

1.2 billion years ago

900 million years ago

435 million years ago

MulticellularityMulticellularity

Evolution of MulticellularityEvolution of Multicellularity

Evolution of MulticellularityEvolution of Multicellularity An experiment that yielded proto-bodies from no-bodies An experiment that yielded proto-bodies from no-bodies

A single-celled alga cultured in the lab for more than a thousand A single-celled alga cultured in the lab for more than a thousand generations.generations.

Always single-celled.Always single-celled. Introduce a single-celled predator that feeds on this alga.Introduce a single-celled predator that feeds on this alga. In <200 generations the alga:In <200 generations the alga:

Becomes clumps of hundreds of cellsBecomes clumps of hundreds of cells Over time the clumps drop to 8 cellsOver time the clumps drop to 8 cells

Eight turns out to be optimum size of clump to:Eight turns out to be optimum size of clump to: 1) Avoid being eaten1) Avoid being eaten 2) While maximizing light availability to all cells2) While maximizing light availability to all cells

When predator was removed it remained an 8-cell colony! When predator was removed it remained an 8-cell colony! Proto-bodies evolved from “no-bodies” in a couple of hundred generations. Proto-bodies evolved from “no-bodies” in a couple of hundred generations.

Borass, M. E. Seale, D.B., Boxhorn, J. 1988. Phagotrophy by a flagellate selects for Borass, M. E. Seale, D.B., Boxhorn, J. 1988. Phagotrophy by a flagellate selects for colonial prey: A possible origin of multi-cellularity. Evolutionary Ecology, 12:153-164. colonial prey: A possible origin of multi-cellularity. Evolutionary Ecology, 12:153-164.

The Cambrian ExplosionThe Cambrian Explosionabout 530 MYBPabout 530 MYBP

The Burgess Shale (British Columbia, Canada) & The Ediacaran Fauna of AustraliaThe Burgess Shale (British Columbia, Canada) & The Ediacaran Fauna of Australia

Mass Extinctions !Mass Extinctions !(left over from Ch 14)(left over from Ch 14)

Great fun, unless of course you’re in one. The biological deck get cleared, Great fun, unless of course you’re in one. The biological deck get cleared, the biosphere changes, there is burst of evolution.the biosphere changes, there is burst of evolution.

The K/T BoundaryThe K/T Boundary65 million years ago65 million years ago

see p. 284see p. 284

Iridium-rich sedimentary layer.Iridium-rich sedimentary layer. Luis Luis (dad, physicist) (dad, physicist) and Walter and Walter (son, geologist) (son, geologist) AlvarezAlvarez

The Iridium Anomaly in the The Iridium Anomaly in the KT Boundary SedimentsKT Boundary Sediments

•This is best picture I could find. This is best picture I could find. •It’s my understanding that It’s my understanding that average Ir was 100 ppm and average Ir was 100 ppm and peak was 3000ppm. peak was 3000ppm. •That’s 30X higher at GubbioThat’s 30X higher at Gubbio•Denmark: 160X, New Zealand: 20XDenmark: 160X, New Zealand: 20X

•But you get the picture !!!But you get the picture !!!

K/T BoundaryK/T Boundary

Foraminifera prior to K-T boundary

Foraminifera from after K-T boundary

The K/T BoundaryThe K/T Boundary65 million years ago65 million years ago

fun with asteroids: click here and get blown awayfun with asteroids: click here and get blown away

Mass ExtinctionsMass Extinctions

Have been major contributors to evolutionary Have been major contributors to evolutionary upheavals.upheavals.

Survive or not survive in a changed world.Survive or not survive in a changed world. Gradualism? Catastrophism? Both?Gradualism? Catastrophism? Both?

Yet another Big E !!Yet another Big E !!

UNIT 2 Slide Set 1UNIT 2 Slide Set 1

ENDENDgo to next setgo to next set