The Origin and Evolution of Life on Earth. When did life begin? Quite early in Earth’s history...

The Origin and Evolution The Origin and Evolution of Life on Earthof Life on Earth

When did life begin?When did life begin?

• Quite early in Earth’s historyQuite early in Earth’s history

• Cannot pinpoint time, but can narrow Cannot pinpoint time, but can narrow down a time period with 3 lines of down a time period with 3 lines of evidenceevidence


• Stromatolites (3.5 bill. Stromatolites (3.5 bill. Yr)Yr)– Rocks with distinctive Rocks with distinctive

layer structurelayer structure

• Look identical to living Look identical to living mats of microbesmats of microbes– Layers of microbes and Layers of microbes and

sedimentsediment– Top layer uses Top layer uses

photosynthesisphotosynthesis– Lower layers use top Lower layers use top

layer’s byproductslayer’s byproducts


• Microfossils dating Microfossils dating to 3.5 billion years to 3.5 billion years agoago

• Difficult to Difficult to distinguish from distinguish from mineral structuresmineral structures

• Analysis shows that Analysis shows that some structures some structures contain organic contain organic carboncarbon-found in at least 3 -found in at least 3

sitessites


• Evidence in Evidence in metamorphic rocks that metamorphic rocks that life existed 3.85 billions life existed 3.85 billions years agoyears ago

• Low CLow C1212/C/C1313 fraction in fraction in rock layers suggests liferock layers suggests life– Biological processes Biological processes

prefer Cprefer C1212 to C to C1313

• Find lower fraction of CFind lower fraction of C1313

– Non-biological processes Non-biological processes have no preference, so have no preference, so find equal amountsfind equal amounts


• Rocks before ~4 billion years old are rare and Rocks before ~4 billion years old are rare and hard to findhard to find

• Time of heavy bombardment ended about Time of heavy bombardment ended about 3.8-4.0 billion years ago3.8-4.0 billion years ago– Last devastating impact between 4.2-3.9 bill. Yr Last devastating impact between 4.2-3.9 bill. Yr

agoago

• Evidence suggests life as long as 3.85 billion Evidence suggests life as long as 3.85 billion years ago and definitely at 3.5 billion years years ago and definitely at 3.5 billion years agoago

• Life rose and dominated the planet between Life rose and dominated the planet between 100-500 million years100-500 million years

Living FossilsLiving Fossils

• DNA used as living fossilDNA used as living fossil

• The more alike the DNA sequence The more alike the DNA sequence between species, the more recent between species, the more recent their divergence and extinction of their divergence and extinction of their common ancestortheir common ancestor

Living FossilsLiving Fossils

• Bacteria and Archaea: genetic material NOT separated Bacteria and Archaea: genetic material NOT separated from rest of cellfrom rest of cell

• Eukarya: DNA separated from rest of cell by Eukarya: DNA separated from rest of cell by membranemembrane

• Extremophiles (live near deep-sea vents or in hot Extremophiles (live near deep-sea vents or in hot springs) closest to root of tree of lifesprings) closest to root of tree of life

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 When evaporated, organic chemical

concentration increases making it easier to concentration increases making it easier to combine complex molecules leading to lifecombine complex molecules leading to life

– Current experiments indicate lack of chemical Current experiments indicate lack of chemical energy sufficient to support lifeenergy sufficient to support life

• Deep-sea vents/hot springsDeep-sea vents/hot springs– DNA evidence suggests that early organisms DNA evidence suggests that early organisms

survived in conditions similar to deep-sea survived in conditions similar to deep-sea ventsvents

– Plenty of chemical energy availablePlenty of chemical energy available

How did life begin?How did life begin?

• Simplest organisms today and those Simplest organisms today and those dated 3.5 billion years ago are dated 3.5 billion years ago are remarkable advancedremarkable advanced

• What are the natural chemical What are the natural chemical processes that could have led to life?processes that could have led to life?

• AssumptionsAssumptions– Life began under chemical conditions of early Life began under chemical conditions of early

EarthEarth– Life did not migrate to EarthLife did not migrate to Earth

Organic Chemistry on Early Organic Chemistry on Early EarthEarth

• In 1920’s, scientists hypothesized In 1920’s, scientists hypothesized that the chemicals in the early that the chemicals in the early atmosphere, fueled by sunlight, atmosphere, fueled by sunlight, would spontaneously create organic would spontaneously create organic moleculesmolecules

• Tested by Miller-Urey experiment Tested by Miller-Urey experiment 1950’s1950’s

Miller-Urey ExperimentMiller-Urey Experiment

• First flask partially filled with water and heated First flask partially filled with water and heated to produce water vapor (sea)to produce water vapor (sea)

• Water vapor was moved to a second flask Water vapor was moved to a second flask where methane and ammonia vapor was where methane and ammonia vapor was added (atmosphere)added (atmosphere)

• Electric sparks (lightening) in second flask was Electric 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 Result: turned brown with amino acids and other complex organic moleculesother complex organic molecules

Time to think……Time to think……

We have discussed the formation of We have discussed the formation of the solar system and the formation the solar system and the formation of the terrestrial planets. Now, what of the terrestrial planets. Now, what is wrong with the Miller-Urey is wrong with the Miller-Urey experiment?experiment?

Variations of Miller-Urey Variations of Miller-Urey ExperimentExperiment

• Different mixes of gases to represent Different mixes of gases to represent atmosphereatmosphere

• Different energy sources, like UV Different energy sources, like UV (sunlight)(sunlight)

• Results: ALL PRODUCE AMINO ACIDS Results: 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 MUST be more sources of organic

materialmaterial

Sources of Organic Sources of Organic MoleculesMolecules• 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 and Chemical analysis of comets and

carbonaceous chondrites show that they carbonaceous chondrites show that they have organic moleculeshave organic molecules

• Chemical reactions near deep-sea ventsChemical reactions near deep-sea vents– Heat from undersea volcano can fuel Heat from undersea volcano can fuel

chemical reactions between water and chemical reactions between water and mineralsminerals

Transition from chemistry to Transition from chemistry to biologybiology• Organic molecules are building Organic molecules are building

blocks of life. blocks of life.

• Low probability of forming life even if Low probability of forming life even if repeated several times.repeated several times.

• Intermediate steps of high probability Intermediate steps of high probability are necessaryare necessary

Search for Self-Replicating Search for Self-Replicating MoleculeMolecule

• Work backward from organisms that Work backward from organisms that live todaylive today

• DNA is double-stranded = complicatedDNA is double-stranded = complicated• RNA obvious candidate, more simple RNA obvious candidate, more simple

than DNAthan DNA– 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

Search for Self-Replicating Search for Self-Replicating MoleculeMolecule

• Problem: RNA and DNA require Problem: RNA and DNA require enzymes to replicateenzymes to replicate

• In 1980’s determined that RNA might In 1980’s determined that RNA might catalyze their own replication instead catalyze their own replication instead of other enzymesof other enzymes

• Early Earth was an RNA-worldEarly Earth was an RNA-world

Search for Replicating Search for Replicating MoleculeMolecule• On Early Earth, short strands of RNA-like On Early Earth, short strands of RNA-like

molecules were produced spontaneously molecules were produced spontaneously partially or completelypartially or completely

• RNA-like molecules that could replicate RNA-like molecules that could replicate faster with less errors soon dominated faster with less errors soon dominated populationpopulation

• Copying errors introduced mutations, Copying errors introduced mutations, ensuring the production of many ensuring the production of many variations of successful moleculesvariations of successful molecules

• 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

Assembling Complex Organic Assembling Complex Organic MoleculesMolecules

• Organic soup was too dilute to favor the Organic soup was too dilute to favor the creation of complex organic moleculescreation of complex organic molecules

• Lab experiment with possible solution: Lab experiment with possible solution: When hot sand, clay or rock is placed in When hot sand, clay or rock is placed in dilute organic solution, complex molecules dilute organic solution, complex molecules self-assembleself-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 Strands of RNA up to 100 bases have been

produced this wayproduced this way

Assembling Complex Organic Assembling Complex Organic MoleculesMolecules

• Other inorganic minerals may have Other inorganic minerals may have also had a similar rolealso had a similar role

• Iron pyrite (fool’s gold)Iron pyrite (fool’s gold)– Positive charges on surface which allows Positive charges on surface which allows

organic molecules to adhereorganic molecules to adhere– Formation of pyrite releases energy Formation of pyrite releases energy

which could be used as fuel for chemical which could be used as fuel for chemical reactionsreactions

Early Cell-like StructuresEarly Cell-like Structures

• Advantages to Advantages to enclosing enzymes enclosing enzymes with RNA moleculeswith RNA molecules

• Close proximity Close proximity increases rate of increases rate of reactions between reactions between themthem

• Isolate contents Isolate contents from outside worldfrom outside world

Early Cell-like StructuresEarly Cell-like Structures

• Lab experiments suggest that Lab experiments suggest that membrane structures existed on membrane structures existed on early Earthearly Earth

• Form spontaneouslyForm spontaneously– Cool down warm-water solution of amino Cool down warm-water solution of amino

acidsacids– Mix lipids (fats) with waterMix lipids (fats) with water

Nonliving Pre-Cells have Nonliving Pre-Cells have Lifelike BehaviorLifelike Behavior

• Grow in size until Grow in size until unstable then split unstable then split to form a ‘daughter’ to form a ‘daughter’ cellcell

• Selectively allow Selectively allow other types of other types of molecules to pass molecules to pass in/out of membranein/out of membrane

• Store energy in the Store energy in the form of electric form of electric voltagevoltage

HandednessHandedness

• Organic molecules come in left- and Organic molecules come in left- and right-handed formsright-handed forms

• Non-biological processes have not Non-biological processes have not preferencepreference

• Biological processes DO have a Biological processes DO have a preferencepreference

• If both left- and right-handed RNA If both left- and right-handed RNA developed, why did one die out?developed, why did one die out?

Quick SummaryQuick Summary

Panspermia?Panspermia?

• Panspermia = life originated Panspermia = life originated elsewhere and migrated to Earthelsewhere and migrated to Earth

• Life began in rock, then kicked off Life began in rock, then kicked off the planet by an impactthe planet by an impact

• Support: organic material is Support: organic material is everywhere, and some bacteria can everywhere, and some bacteria can withstand large amounts of radiation withstand large amounts of radiation and go dormant under low and go dormant under low atmospheric conditionsatmospheric conditions

PanspermiaPanspermia

• 2 schools of thought2 schools of thought• School 1: life did not evolve as easily as School 1: life did not evolve as easily as

imagined on early Earth in timescales imagined on early Earth in timescales we’ve determinedwe’ve determined

• Problem: entire solar system was under Problem: 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 Problem: rock to be ejected out of its

own system, then fall into ours and hit own system, then fall into ours and hit the tiny planet of Earththe tiny planet of Earth


• School 2: life evolved easily and was School 2: life evolved easily and was everywhere with suitable conditionseverywhere with suitable conditions

• Earth was not first planet with Earth was not first planet with suitable conditionssuitable conditions

• Migration of life from another planet Migration of life from another planet (say Mars) dominated before early (say Mars) dominated before early life on Earth couldlife on Earth could– We’re Martians!!!!We’re Martians!!!!


• Martian meteoritesMartian meteorites

• Both have possible Both have possible fossil evidence of fossil evidence of life on Marslife on Mars

Living cyanobacteria Microfossils in carbonaceous chondrites


Work out Exercise I. When, Where Work out Exercise I. When, Where and How? in the class activity and How? in the class activity ‘Origins of Life on Earth’.‘Origins of Life on Earth’.

Early Evolution and Rise of Early Evolution and Rise of OO22

• First organisms had simple metabolismFirst organisms had simple metabolism• Atmosphere was OAtmosphere was O22 free, must have free, must have

been anaerobicbeen anaerobic• 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 Modern archaea appear to be close to the root of the tree of lifeof the tree of life

•Obtaining energy from chemical reactions Obtaining energy from chemical reactions involving hydrogen, sulfur and iron compounds involving hydrogen, sulfur and iron compounds (all abundant on early Earth)(all abundant on early Earth)

Early EvolutionEarly Evolution

• Natural selection probably resulted in Natural selection probably resulted in rapid diversificationrapid diversification

• Modern DNA has enzymes that Modern DNA has enzymes that reduce the rate of mutationsreduce the rate of mutations

• RNA is not so lucky, more likely to RNA is not so lucky, more likely to have copying errorshave copying errors

• Higher mutation rate in early Higher mutation rate in early evolution than nowevolution than now

PhotosynthesisPhotosynthesis

• Most important new metabolic process Most important new metabolic process evolved graduallyevolved gradually

• Organisms that lived close to ocean surface Organisms that lived close to ocean surface probably developed means of absorbing probably developed means of absorbing sunlight (UV in particular)sunlight (UV in particular)

• Once absorbed, developed method of Once absorbed, developed method of turning it into energyturning it into energy– Modern organisms of purple sulfur bacteria and Modern organisms of purple sulfur bacteria and

green sulfur bacteria much like early green sulfur bacteria much like early photosynthetic microbes, use H2S instead of photosynthetic microbes, use H2S instead of H2O for photosynthesisH2O for photosynthesis

PhotosynthesisPhotosynthesis

• Using water for photosynthesis developed later, Using water for photosynthesis developed later, perhaps 3.5 billion years agoperhaps 3.5 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!

Rise of ORise of O22• OO22 is highly reactive is highly reactive• All initial OAll initial O22 would react with rock and would react with rock and

minerals in waterminerals in water• OO22 could not accumulate in atmosphere until could not accumulate in atmosphere until

surface rock was saturatedsurface rock was saturated• Rocks 2-3 bill. Yr old called banded iron Rocks 2-3 bill. Yr old called banded iron

formations, show atmosphere had <1% of formations, show atmosphere had <1% of current amount of Ocurrent amount of O22

• Rock evidence suggests that ORock evidence suggests that O22 amounts in amounts in atmosphere began to rise about 2.0 bill. Yr atmosphere began to rise about 2.0 bill. Yr agoago

• Clear evidence of OClear evidence of O22 near current levels near current levels appears only 200 million yr ago appears only 200 million yr ago – Find charcoal (fossil fuel)Find charcoal (fossil fuel)– Indicates enough OIndicates enough O22 in atmosphere for fires to burn in atmosphere for fires to burn

Rise of ORise of O22

• Rise of ORise of O22 would have created a crisis would have created a crisis for lifefor life

• OO22 reacts with bonds of organic reacts with bonds of organic materialsmaterials

• Surviving species avoided effects of OSurviving species avoided effects of O22 because they lived or migrated to because they lived or migrated to underground locationsunderground locations– Many anaerobic microbes found in such Many anaerobic microbes found in such

locales todaylocales today

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 atmosphere rising in atmosphere

• DNA evidence suggests that prokaryotes DNA evidence suggests that prokaryotes and eukaryotes separated from common and eukaryotes separated from common ancestor much earlierancestor much earlier

• OO22 played a key role in eukaryote evolution played a key role in eukaryote evolution– Cells can produce energy more efficiently using Cells can produce energy more efficiently using

aerobic metabolism than anaerobic metabolismaerobic metabolism than anaerobic metabolism– Adaptations of aerobic organisms could develop Adaptations of aerobic organisms could develop

adaptations that required more energy that adaptations that required more energy that would be available for anaerobic organismswould be available for anaerobic organisms

The Cambrian ExplosionThe Cambrian Explosion

• Animal branch of the tree of lifeAnimal branch of the tree of life

• Different classifications based on Different classifications based on body planbody plan

• All known body plans made All known body plans made appearance in fossil record in a time appearance in fossil record in a time span of 40 million yearsspan of 40 million years– <1% of Earth’s age<1% of Earth’s age– Animal diversity began 545 mill. Yr agoAnimal diversity began 545 mill. Yr ago

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 solar Had 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 could Natural selection favored that which could

withstand periods of droughtwithstand periods of drought

Colonization of LandColonization of Land

• DNA evidence suggests that plants DNA evidence suggests that plants evolved from an algaeevolved from an algae

• It took only 75 mill. Yrs for animals to It took only 75 mill. Yrs for animals to follow plants out of waterfollow plants out of water

Mass ExtinctionsMass Extinctions

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 Suspected for Permian extinction 245 mill yr agoago

– Active volcanismActive volcanism•Climate changeClimate change

– External influence for copying errorsExternal influence for copying errors• Increase in solar particles or radiation hitting Increase in solar particles or radiation hitting

surfacesurface

•Local supernovaLocal supernova

Primate EvolutionPrimate Evolution

• Monkeys, apes, lemurs and humans have Monkeys, 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 than Offspring would be born more helpless than

other animalsother animals

Emergence of HumansEmergence of Humans

• Did NOT evolve from gorillas or Did NOT evolve from gorillas or monkeysmonkeys

• Share a common ancestor that lived Share a common ancestor that lived just a few million years agojust a few million years ago

• 98% of human genome is identical to 98% of human genome is identical to genome of the chimpanzeegenome of the chimpanzee

• 2% difference in genome separates the 2% difference in genome separates the success of humans verses chimpssuccess of humans verses chimps– Also indicates evolution of intelligence is Also indicates evolution of intelligence is

complex complex


• After hominids diverged from chimps and After hominids diverged from chimps and gorillas, evolution has followed a complex gorillas, evolution has followed a complex pathpath

• Numerous hominids species existed, some Numerous 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 modern First 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 with Our ancestors shared the Earth with NeanderthalsNeanderthals– Went extinct 35,000 years agoWent extinct 35,000 years ago

Cultural and Technological Cultural and Technological EvolutionEvolution• Have not undergone biological evolution in Have 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 Result of coupling between science and

technologytechnology– About 100 years between industrial revolution to About 100 years between industrial revolution to

landing on the Moon and generating weapons of landing on the Moon and generating weapons of mass destructionmass destruction


Work out Exercise II. From Microbes Work out Exercise II. From Microbes to Complex Organisms in class to Complex Organisms in class activity ‘Origins of Life on Earth’.activity ‘Origins of Life on Earth’.

The Origin and Evolution of Life on Earth. When did life begin? Quite early in Earth’s history...

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