This presentation discusses the possible Origins of Life on Earth,

1. The Origin and Evolution ofThe Origin and Evolution of
Life on EarthLife on Earth

2. When did life begin?When did life begin?
• Quite early in Earth’s historyQuite early in Earth’s history
• Cannot pinpoint time, but can narrowCannot pinpoint time, but can narrow
down a time period with 3 lines ofdown a time period with 3 lines of
evidenceevidence

3. When did life begin?When did life begin?
• Stromatolites (3.5 bill. Yr)Stromatolites (3.5 bill. Yr)
– Rocks with distinctive layerRocks with distinctive layer
structurestructure
• Look identical to livingLook identical to living
mats of microbesmats of microbes
– Layers of microbes andLayers of microbes and
sedimentsediment
– Top layer usesTop layer uses
photosynthesisphotosynthesis
– Lower layers use topLower layers use top
layer’s byproductslayer’s byproducts

4. When did life begin?When did life begin?
• Microfossils dating toMicrofossils dating to
3.5 billion years ago3.5 billion years ago
• Difficult to distinguishDifficult to distinguish
from mineralfrom mineral
structuresstructures
• Analysis shows thatAnalysis shows that
some structuressome structures
contain organiccontain organic
carboncarbon
-found in at least 3 sites-found in at least 3 sites

5. When did life begin?When did life begin?
• Evidence in metamorphicEvidence in metamorphic
rocks that life existedrocks that life existed
3.85 billions years ago3.85 billions years ago
• Low CLow C1212
/C/C1313
fraction in rockfraction in rock
layers suggests lifelayers suggests life
– Biological processes preferBiological processes prefer
CC1212
to Cto C1313
• Find lower fraction of CFind lower fraction of C1313
– Non-biological processesNon-biological processes
have no preference, so findhave no preference, so find
equal amountsequal amounts

6. When did life begin?When did life begin?
• Rocks before ~4 billion years old are rare andRocks before ~4 billion years old are rare and
hard to findhard to find
• Time of heavy bombardment ended about 3.8-Time of heavy bombardment ended about 3.8-
4.0 billion years ago4.0 billion years ago
– Last devastating impact between 4.2-3.9 bill. Yr agoLast devastating impact between 4.2-3.9 bill. Yr ago
• Evidence suggests life as long as 3.85 billionEvidence suggests life as long as 3.85 billion
years ago and definitely at 3.5 billion years agoyears ago and definitely at 3.5 billion years ago
• Life rose and dominated the planet betweenLife rose and dominated the planet between
100-500 million years100-500 million years

7. Living FossilsLiving Fossils
• DNA used as living fossilDNA used as living fossil
• The more alike the DNA sequenceThe more alike the DNA sequence
between species, the more recent theirbetween species, the more recent their
divergence and extinction of their commondivergence and extinction of their common
ancestorancestor

8. Living FossilsLiving Fossils
• Bacteria and Archaea: genetic material NOT separatedBacteria and Archaea: genetic material NOT separated
from rest of cellfrom rest of cell
• Eukarya: DNA separated from rest of cell by membraneEukarya: DNA separated from rest of cell by membrane
• Extremophiles (live near deep-sea vents or in hotExtremophiles (live near deep-sea vents or in hot
springs) closest to root of tree of lifesprings) closest to root of tree of life

9. Where did life begin?Where did life begin?
• Land is unlikelyLand is unlikely
– No ONo O22, no ozone: UV destroys molecular bonds, no ozone: UV destroys molecular bonds
• Shallow pondsShallow ponds
– Once favored, full of organic materialOnce favored, full of organic material
– When evaporated, organic chemical concentrationWhen evaporated, organic chemical concentration
increases making it easier to combine complexincreases making it easier to combine complex
molecules leading to lifemolecules leading to life
– Current experiments indicate lack of chemical energyCurrent experiments indicate lack of chemical energy
sufficient to support lifesufficient to support life
• Deep-sea vents/hot springsDeep-sea vents/hot springs
– DNA evidence suggests that early organisms survivedDNA evidence suggests that early organisms survived
in conditions similar to deep-sea ventsin conditions similar to deep-sea vents
– Plenty of chemical energy availablePlenty of chemical energy available

10. How did life begin?How did life begin?
• Simplest organisms today and those datedSimplest organisms today and those dated
3.5 billion years ago are remarkable3.5 billion years ago are remarkable
advancedadvanced
• What are the natural chemical processesWhat are the natural chemical processes
that could have led to life?that could have led to life?
• AssumptionsAssumptions
– Life began under chemical conditions of early EarthLife began under chemical conditions of early Earth
– Life did not migrate to EarthLife did not migrate to Earth

11. Organic Chemistry on Early EarthOrganic Chemistry on Early Earth
• In 1920’s, scientists hypothesized that theIn 1920’s, scientists hypothesized that the
chemicals in the early atmosphere, fueledchemicals in the early atmosphere, fueled
by sunlight, would spontaneously createby sunlight, would spontaneously create
organic moleculesorganic molecules
• Tested by Miller-Urey experiment 1950’sTested by Miller-Urey experiment 1950’s

12. Miller-Urey ExperimentMiller-Urey Experiment
• First flask partially filled with water and heated toFirst flask partially filled with water and heated to
produce water vapor (sea)produce water vapor (sea)
• Water vapor was moved to a second flask whereWater vapor was moved to a second flask where
methane and ammonia vapor was addedmethane and ammonia vapor was added
(atmosphere)(atmosphere)
• Electric sparks (lightening) in second flask wasElectric sparks (lightening) in second flask was
energy source for chemical reactionsenergy source for chemical reactions
• Below second flask, water vapor cooled (rain)Below second flask, water vapor cooled (rain)
and recycled to first flask (sea)and recycled to first flask (sea)
• Result: turned brown with amino acids and otherResult: turned brown with amino acids and other
complex organic moleculescomplex organic molecules

14. Time to think……Time to think……
We have discussed the formation of theWe have discussed the formation of the
solar system and the formation of thesolar system and the formation of the
terrestrial planets. Now, what is wrongterrestrial planets. Now, what is wrong
with the Miller-Urey experiment?with the Miller-Urey experiment?

15. Variations of Miller-UreyVariations of Miller-Urey
ExperimentExperiment
• Different mixes of gases to representDifferent mixes of gases to represent
atmosphereatmosphere
• Different energy sources, like UVDifferent energy sources, like UV
(sunlight)(sunlight)
• Results: ALL PRODUCE AMINO ACIDSResults: ALL PRODUCE AMINO ACIDS
AND COMPLEX ORGANIC MOLECULESAND COMPLEX ORGANIC MOLECULES
– Not as much as original experimentNot as much as original experiment
– MUST be more sources of organic materialMUST be more sources of organic material

16. Sources of Organic MoleculesSources of Organic Molecules
• Chemical reactions in atmosphereChemical reactions in atmosphere
– Lab experiments show this is likelyLab experiments show this is likely
• Organic material brought by impactsOrganic material brought by impacts
– Chemical analysis of comets andChemical analysis of comets and
carbonaceous chondrites show that they havecarbonaceous chondrites show that they have
organic moleculesorganic molecules
• Chemical reactions near deep-sea ventsChemical reactions near deep-sea vents
– Heat from undersea volcano can fuelHeat from undersea volcano can fuel
chemical reactions between water andchemical reactions between water and
mineralsminerals

17. Transition from chemistry to biologyTransition from chemistry to biology
• Organic molecules are building blocks ofOrganic molecules are building blocks of
life.life.
• Low probability of forming life even ifLow probability of forming life even if
repeated several times.repeated several times.
• Intermediate steps of high probability areIntermediate steps of high probability are
necessarynecessary

18. Search for Self-ReplicatingSearch for Self-Replicating
MoleculeMolecule
• Work backward from organisms that liveWork backward from organisms that live
todaytoday
• DNA is double-stranded = complicatedDNA is double-stranded = complicated
• RNA obvious candidate, more simple thanRNA obvious candidate, more simple than
DNADNA
– Hereditary informationHereditary information
– Can serve as template for replicationCan serve as template for replication
– Fewer steps to produce backbone structureFewer steps to produce backbone structure

19. Search for Self-ReplicatingSearch for Self-Replicating
MoleculeMolecule
• Problem: RNA and DNA require enzymesProblem: RNA and DNA require enzymes
to replicateto replicate
• In 1980’s determined that RNA mightIn 1980’s determined that RNA might
catalyze their own replication instead ofcatalyze their own replication instead of
other enzymesother enzymes
• Early Earth was an RNA-worldEarly Earth was an RNA-world

20. Search for Replicating MoleculeSearch for Replicating Molecule
• On Early Earth, short strands of RNA-likeOn Early Earth, short strands of RNA-like
molecules were produced spontaneouslymolecules were produced spontaneously
partially or completelypartially or completely
• RNA-like molecules that could replicate fasterRNA-like molecules that could replicate faster
with less errors soon dominated populationwith less errors soon dominated population
• Copying errors introduced mutations, ensuringCopying errors introduced mutations, ensuring
the production of many variations of successfulthe production of many variations of successful
moleculesmolecules
• Allowed molecular evolution to continueAllowed molecular evolution to continue
• RNA-world gave way to DNA-worldRNA-world gave way to DNA-world
– DNA less prone to copying errorsDNA less prone to copying errors
– DNA more flexible hereditary materialDNA more flexible hereditary material
– RNA kept some of its original functionsRNA kept some of its original functions

21. Assembling Complex OrganicAssembling Complex Organic
MoleculesMolecules
• Organic soup was too dilute to favor the creationOrganic soup was too dilute to favor the creation
of complex organic moleculesof complex organic molecules
• Lab experiment with possible solution: WhenLab experiment with possible solution: When
hot sand, clay or rock is placed in dilute organichot sand, clay or rock is placed in dilute organic
solution, complex molecules self-assemblesolution, complex molecules self-assemble
– Organic molecules stick to surface of clayOrganic molecules stick to surface of clay
– Increases density and likelihood of reactionsIncreases density and likelihood of reactions
– Strands of RNA up to 100 bases have been producedStrands of RNA up to 100 bases have been produced
this waythis way

22. Assembling Complex OrganicAssembling Complex Organic
MoleculesMolecules
• Other inorganic minerals may have alsoOther inorganic minerals may have also
had a similar rolehad a similar role
• Iron pyrite (fool’s gold)Iron pyrite (fool’s gold)
– Positive charges on surface which allowsPositive charges on surface which allows
organic molecules to adhereorganic molecules to adhere
– Formation of pyrite releases energy whichFormation of pyrite releases energy which
could be used as fuel for chemical reactionscould be used as fuel for chemical reactions

23. Early Cell-like StructuresEarly Cell-like Structures
• Advantages toAdvantages to
enclosing enzymesenclosing enzymes
with RNA moleculeswith RNA molecules
• Close proximityClose proximity
increases rate ofincreases rate of
reactions betweenreactions between
themthem
• Isolate contents fromIsolate contents from
outside worldoutside world

24. Early Cell-like StructuresEarly Cell-like Structures
• Lab experiments suggest that membraneLab experiments suggest that membrane
structures existed on early Earthstructures existed on early Earth
• Form spontaneouslyForm spontaneously
– Cool down warm-water solution of aminoCool down warm-water solution of amino
acidsacids
– Mix lipids (fats) with waterMix lipids (fats) with water

25. Nonliving Pre-Cells have LifelikeNonliving Pre-Cells have Lifelike
BehaviorBehavior
• Grow in size untilGrow in size until
unstable then split tounstable then split to
form a ‘daughter’ cellform a ‘daughter’ cell
• Selectively allowSelectively allow
other types ofother types of
molecules to passmolecules to pass
in/out of membranein/out of membrane
• Store energy in theStore energy in the
form of electricform of electric
voltagevoltage

26. HandednessHandedness
• Organic molecules come in left- and right-Organic molecules come in left- and right-
handed formshanded forms
• Non-biological processes have notNon-biological processes have not
preferencepreference
• Biological processes DO have aBiological processes DO have a
preferencepreference
• If both left- and right-handed RNAIf both left- and right-handed RNA
developed, why did one die out?developed, why did one die out?

27. Quick SummaryQuick Summary

28. Panspermia?Panspermia?
• Panspermia = life originated elsewherePanspermia = life originated elsewhere
and migrated to Earthand migrated to Earth
• Life began in rock, then kicked off theLife began in rock, then kicked off the
planet by an impactplanet by an impact
• Support: organic material is everywhere,Support: organic material is everywhere,
and some bacteria can withstand largeand some bacteria can withstand large
amounts of radiation and go dormantamounts of radiation and go dormant
under low atmospheric conditionsunder low atmospheric conditions

29. PanspermiaPanspermia
• 2 schools of thought2 schools of thought
• School 1: life did not evolve as easily asSchool 1: life did not evolve as easily as
imagined on early Earth in timescalesimagined on early Earth in timescales
we’ve determinedwe’ve determined
• Problem: entire solar system was underProblem: entire solar system was under
heavy bombardment at the same timeheavy bombardment at the same time
• Other possibility: interstellar migrationOther possibility: interstellar migration
• Problem: rock to be ejected out of its ownProblem: rock to be ejected out of its own
system, then fall into ours and hit the tinysystem, then fall into ours and hit the tiny
planet of Earthplanet of Earth

30. PanspermiaPanspermia
• School 2: life evolved easily and wasSchool 2: life evolved easily and was
everywhere with suitable conditionseverywhere with suitable conditions
• Earth was not first planet with suitableEarth was not first planet with suitable
conditionsconditions
• Migration of life from another planet (sayMigration of life from another planet (say
Mars) dominated before early life on EarthMars) dominated before early life on Earth
couldcould
– We’re Martians!!!!We’re Martians!!!!

31. PanspermiaPanspermia
• Martian meteoritesMartian meteorites
• Both have possibleBoth have possible
fossil evidence of lifefossil evidence of life
on Marson Mars

32. Living cyanobacteria Microfossils in carbonaceous chondrites

33. Time to think……Time to think……
Work out Exercise I. When, Where andWork out Exercise I. When, Where and
How? in the class activity ‘Origins of LifeHow? in the class activity ‘Origins of Life
on Earth’.on Earth’.

34. Early Evolution and Rise of OEarly Evolution and Rise of O22
• First organisms had simple metabolismFirst organisms had simple metabolism
• Atmosphere was OAtmosphere was O22 free, must have beenfree, must have been
anaerobicanaerobic
• Probably chemoheterotrophsProbably chemoheterotrophs
– Obtained nutrients from organic materialObtained nutrients from organic material
– Obtained nutrients from inorganic materialObtained nutrients from inorganic material
• Modern archaea appear to be close to the root ofModern archaea appear to be close to the root of
the tree of lifethe tree of life
• Obtaining energy from chemical reactions involvingObtaining energy from chemical reactions involving
hydrogen, sulfur and iron compounds (all abundanthydrogen, sulfur and iron compounds (all abundant
on early Earth)on early Earth)

35. Early EvolutionEarly Evolution
• Natural selection probably resulted inNatural selection probably resulted in
rapid diversificationrapid diversification
• Modern DNA has enzymes that reduce theModern DNA has enzymes that reduce the
rate of mutationsrate of mutations
• RNA is not so lucky, more likely to haveRNA is not so lucky, more likely to have
copying errorscopying errors
• Higher mutation rate in early evolutionHigher mutation rate in early evolution
than nowthan now

36. PhotosynthesisPhotosynthesis
• Most important new metabolic process evolvedMost important new metabolic process evolved
graduallygradually
• Organisms that lived close to ocean surfaceOrganisms that lived close to ocean surface
probably developed means of absorbing sunlightprobably developed means of absorbing sunlight
(UV in particular)(UV in particular)
• Once absorbed, developed method of turning itOnce absorbed, developed method of turning it
into energyinto energy
– Modern organisms of purple sulfur bacteria and greenModern organisms of purple sulfur bacteria and green
sulfur bacteria much like early photosyntheticsulfur bacteria much like early photosynthetic
microbes, use H2S instead of H2O for photosynthesismicrobes, use H2S instead of H2O for photosynthesis

37. PhotosynthesisPhotosynthesis
• Using water for photosynthesis developed later, perhapsUsing water for photosynthesis developed later, perhaps
3.5 billion years ago3.5 billion years ago
• First appearing in cyanobacteria (blue-green algae)First appearing in cyanobacteria (blue-green algae)
• By product of OBy product of O22, released into atmosphere, released into atmosphere
• Changed the world!Changed the world!

38. Rise of ORise of O22
• OO22 is highly reactiveis highly reactive
• All initial OAll initial O22 would react with rock and minerals inwould react with rock and minerals in
waterwater
• OO22 could not accumulate in atmosphere untilcould not accumulate in atmosphere until
surface rock was saturatedsurface rock was saturated
• Rocks 2-3 bill. Yr old called banded ironRocks 2-3 bill. Yr old called banded iron
formations, show atmosphere had <1% offormations, show atmosphere had <1% of
current amount of Ocurrent amount of O22
• Rock evidence suggests that ORock evidence suggests that O22 amounts inamounts in
atmosphere began to rise about 2.0 bill. Yr agoatmosphere began to rise about 2.0 bill. Yr ago
• Clear evidence of OClear evidence of O22 near current levels appearsnear current levels appears
only 200 million yr agoonly 200 million yr ago
– Find charcoal (fossil fuel)Find charcoal (fossil fuel)

39. Rise of ORise of O22
• Rise of ORise of O22 would have created a crisis forwould have created a crisis for
lifelife
• OO22 reacts with bonds of organic materialsreacts with bonds of organic materials
• Surviving species avoided effects of OSurviving species avoided effects of O22
because they lived or migrated tobecause they lived or migrated to
underground locationsunderground locations
– Many anaerobic microbes found in suchMany anaerobic microbes found in such
locales todaylocales today

40. Early EukaryotesEarly Eukaryotes
• Fossil evidence dates to 2.1 bill. Yr agoFossil evidence dates to 2.1 bill. Yr ago
• Dates to when ODates to when O22 rising in atmosphererising in atmosphere
• DNA evidence suggests that prokaryotes andDNA evidence suggests that prokaryotes and
eukaryotes separated from common ancestoreukaryotes separated from common ancestor
much earliermuch earlier
• OO22 played a key role in eukaryote evolutionplayed a key role in eukaryote evolution
– Cells can produce energy more efficiently usingCells can produce energy more efficiently using
aerobic metabolism than anaerobic metabolismaerobic metabolism than anaerobic metabolism
– Adaptations of aerobic organisms could developAdaptations of aerobic organisms could develop
adaptations that required more energy that would beadaptations that required more energy that would be
available for anaerobic organismsavailable for anaerobic organisms

41. The Cambrian ExplosionThe Cambrian Explosion
• Animal branch of the tree of lifeAnimal branch of the tree of life
• Different classifications based on bodyDifferent classifications based on body
planplan
• All known body plans made appearance inAll known body plans made appearance in
fossil record in a time span of 40 millionfossil record in a time span of 40 million
yearsyears
– <1% of Earth’s age<1% of Earth’s age
– Animal diversity began 545 mill. Yr agoAnimal diversity began 545 mill. Yr ago

42. Colonization of LandColonization of Land
• Life flourished where liquid water existLife flourished where liquid water exist
• Life on land was more complicatedLife on land was more complicated
– Had to develop means of collecting solarHad to develop means of collecting solar
energy above ground and nutrients belowenergy above ground and nutrients below
• Life in shallow ponds or edges of lakesLife in shallow ponds or edges of lakes
– Water evaporatesWater evaporates
– Natural selection favored that which couldNatural selection favored that which could
withstand periods of droughtwithstand periods of drought

43. Colonization of LandColonization of Land
• DNA evidence suggests that plants evolved fromDNA evidence suggests that plants evolved from
an algaean algae
• It took only 75 mill. Yrs for animals to followIt took only 75 mill. Yrs for animals to follow
plants out of waterplants out of water

44. Mass ExtinctionsMass Extinctions

45. Mass ExtinctionsMass Extinctions
• Possible CausesPossible Causes
– ImpactsImpacts
• Impact sites found for K-T boundaryImpact sites found for K-T boundary
• Suspected for Permian extinction 245 mill yr agoSuspected for Permian extinction 245 mill yr ago
– Active volcanismActive volcanism
• Climate changeClimate change
– External influence for copying errorsExternal influence for copying errors
• Increase in solar particles or radiation hittingIncrease in solar particles or radiation hitting
surfacesurface
• Local supernovaLocal supernova

46. Primate EvolutionPrimate Evolution
• Monkeys, apes, lemurs and humans haveMonkeys, apes, lemurs and humans have
common ancestor that lived in treescommon ancestor that lived in trees
• Tree lifeTree life
– Limber arms for swinging between branchesLimber arms for swinging between branches
– Eyes in front of head for depth perceptionEyes in front of head for depth perception
– Offspring would be born more helpless thanOffspring would be born more helpless than
other animalsother animals

47. Emergence of HumansEmergence of Humans
• Did NOT evolve from gorillas or monkeysDid NOT evolve from gorillas or monkeys
• Share a common ancestor that lived just aShare a common ancestor that lived just a
few million years agofew million years ago
• 98% of human genome is identical to98% of human genome is identical to
genome of the chimpanzeegenome of the chimpanzee
• 2% difference in genome separates the2% difference in genome separates the
success of humans verses chimpssuccess of humans verses chimps
– Also indicates evolution of intelligence isAlso indicates evolution of intelligence is
complexcomplex

48. Emergence of HumansEmergence of Humans

49. Emergence of HumansEmergence of Humans
• After hominids diverged from chimps andAfter hominids diverged from chimps and
gorillas, evolution has followed a complex pathgorillas, evolution has followed a complex path
• Numerous hominids species existed, someNumerous hominids species existed, some
during the same time periodduring the same time period
– All humans are the same speciesAll humans are the same species
• First skull fossils that are identical to modernFirst skull fossils that are identical to modern
human skulls dates to 100,000 yr oldhuman skulls dates to 100,000 yr old
• Our ancestors shared the Earth withOur ancestors shared the Earth with
NeanderthalsNeanderthals
– Went extinct 35,000 years agoWent extinct 35,000 years ago

50. Emergence of HumansEmergence of Humans

51. Cultural and TechnologicalCultural and Technological
EvolutionEvolution
• Have not undergone biological evolution inHave not undergone biological evolution in
40,000 years40,000 years
– Mutation rates are slowMutation rates are slow
• Dramatic cultural changesDramatic cultural changes
– Transmission of knowledge between generationsTransmission of knowledge between generations
• Spoken to written word, thousands of yearsSpoken to written word, thousands of years
• agricultureagriculture
• Technological evolutionTechnological evolution
– Result of coupling between science and technologyResult of coupling between science and technology
– About 100 years between industrial revolution toAbout 100 years between industrial revolution to
landing on the Moon and generating weapons oflanding on the Moon and generating weapons of
mass destructionmass destruction