Origin of Life Biogenesis Earth’s History The First Life-forms

Origin of LifeOrigin of Life

BiogenesisBiogenesisEarth’s HistoryEarth’s HistoryThe First Life-formsThe First Life-forms

Biological EvolutionBiological Evolution

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BiogenesisBiogenesis

• The Concept of Spontaneous The Concept of Spontaneous GenerationGeneration

• Redi’s ExperimentRedi’s Experiment• Spallanzani’s ExperimentSpallanzani’s Experiment• Pasteur’s Experiment Pasteur’s Experiment

Learning ObjectivesLearning Objectives

• TSW…TSW…1.1. Define Define spontaneous generationspontaneous generation, & list , & list

some of the observations that led people some of the observations that led people to think that life could arise from nonliving to think that life could arise from nonliving thingsthings

2.2. Summarize the results of experiments by Summarize the results of experiments by RediRedi & by & by SpallanzaniSpallanzani that tested the that tested the hypothesis of spontaneous generationhypothesis of spontaneous generation

3.3. Describe how Describe how Pasteur’sPasteur’s experiment experiment disproved the hypothesis of spontaneous disproved the hypothesis of spontaneous generationgeneration

Spontaneous GenerationSpontaneous Generation

• Concept that living things could Concept that living things could arise from non-living thingsarise from non-living things Examples Examples

Maggots appear on rotting meatMaggots appear on rotting meatFish & tadpoles appear in formerly dry Fish & tadpoles appear in formerly dry

ponds ponds

• BiogenesisBiogenesis All living things arise from other living All living things arise from other living

thingsthings Cell theoryCell theory

Redi’s ExperimentRedi’s ExperimentFrancesco Redi (1626 – 1697)Francesco Redi (1626 – 1697)

• ProblemProblem How do maggot life arise in rotting meat?How do maggot life arise in rotting meat?

• ObservationObservation Flies land on rotting meatFlies land on rotting meat Maggots appear in rotting meatMaggots appear in rotting meat

• HypothesisHypothesis Maggots arise from the eggs of fliesMaggots arise from the eggs of flies

Redi’s Experiment:Redi’s Experiment:16681668

• InvestigationInvestigation Control groupControl group – meat in – meat in open jarsopen jars: : exposed exposed

to fliesto flies Experimental groupExperimental group – meat in muslin – meat in muslin sealed sealed

jarsjars: : nono contact w/ flies contact w/ flies• DataData

Meat in open jarsMeat in open jars – developed – developed maggotsmaggots Meat in sealed jarsMeat in sealed jars – – nono maggots maggots appear appear

• ConclusionConclusion Maggots hatch from fly eggs laid on rotten Maggots hatch from fly eggs laid on rotten

meatmeat • CriticismCriticism

Did not address microorganismsDid not address microorganisms

Spallanzani’s ExperimentSpallanzani’s ExperimentLazzaro Spallanzani (1729 – 1799)Lazzaro Spallanzani (1729 – 1799)

• ProblemProblem Where do microorganisms come from?Where do microorganisms come from?

• ObservationObservation Broth exposed to air develops Broth exposed to air develops

microorganisms & spoilsmicroorganisms & spoils Microorganisms can be carried into the air Microorganisms can be carried into the air

on duston dust

• HypothesisHypothesis Microorganisms arise from other Microorganisms arise from other

microorganismsmicroorganisms

Spallanzani’s Experiment:Spallanzani’s Experiment:17681768• InvestigationInvestigation

Control groupControl group – boiled broth left in – boiled broth left in open flaskopen flask: : exposed to dustexposed to dust in airin air

Experimental groupExperimental group – boiled broth in – boiled broth in sealed sealed flaskflask: : nono exposure to dust exposure to dust

• DataData Broth in open flasksBroth in open flasks – developed – developed microbesmicrobes Broth in sealed flasksBroth in sealed flasks – – nono microbes microbes appear appear

• ConclusionConclusion Microorganisms arise from other Microorganisms arise from other

microorganismsmicroorganisms • Criticism Criticism –– Sealed flasks deprived of a Sealed flasks deprived of a vital forcevital force

Pasteur’s ExperimentPasteur’s ExperimentLouis Pasteur (1822 – 1895)Louis Pasteur (1822 – 1895)

• ProblemProblem Where do microorganisms come from?Where do microorganisms come from?

• ObservationObservation Broth exposed to air develops Broth exposed to air develops

microorganisms & spoilsmicroorganisms & spoils Microorganisms can be carried into the air Microorganisms can be carried into the air

on duston dust

• HypothesisHypothesis Microorganisms arise from other Microorganisms arise from other

microorganismsmicroorganisms

Pasteur’s Experiment:Pasteur’s Experiment:1859 1859 • InvestigationInvestigation

Control groupControl group – boiled broth left in – boiled broth left in open curve-open curve-necked flasknecked flask: : dustdust in air is in air is trapped by necktrapped by neck

Experimental groupExperimental group – boiled broth is exposed by – boiled broth is exposed by breaking necks: breaking necks: exposure to dustexposure to dust

• DataData Broth in open flasksBroth in open flasks – developed no – developed no microbes for 1 microbes for 1

yearyear Broth in flasks w/ broken neckBroth in flasks w/ broken neck – – microbesmicrobes appear appear

right awayright away• ConclusionConclusion

Microorganisms arise from other Microorganisms arise from other microorganismsmicroorganisms

• No Criticism No Criticism – – Vital force concept abandonedVital force concept abandoned

Earth’s HistoryEarth’s History

• The Formation of the EarthThe Formation of the Earth• The First Organic CompoundsThe First Organic Compounds• From Molecules to Cell-like From Molecules to Cell-like

StructuresStructures


• TSW…TSW…1.1. Outline the modern scientific Outline the modern scientific

understanding of the understanding of the formation of formation of EarthEarth

2.2. Summarize the concept of Summarize the concept of half-lifehalf-life3.3. Describe the production of organic Describe the production of organic

compounds in the compounds in the Miller-Urey Miller-Urey experimentsexperiments

4.4. Summarize the possible importance Summarize the possible importance of of cell-like structures produced in the cell-like structures produced in the laboratorylaboratory

The Formation of the EarthThe Formation of the Earth

• 5 by5 by – – Solar system is swirling mass of Solar system is swirling mass of gas & dustgas & dust Inward collapse of most material: Inward collapse of most material: sun forms sun forms

PlanetsPlanets form from remainder form from remainder

• 4.6 by4.6 by – – Earth formedEarth formed 400 million year period of collisions of 400 million year period of collisions of

planetesimalsplanetesimals Earth is molten due to release of heat energy from Earth is molten due to release of heat energy from

collisionscollisionsEvidence from moon rocks & meteorites Evidence from moon rocks & meteorites

Earth’s AgeEarth’s AgeVolcanismVolcanism

• 4 by4 by – – PlanetesimalPlanetesimal collisions subside collisions subside Volcanic activity begins to form primitive Volcanic activity begins to form primitive

atmosphereatmosphere • 3.8 by3.8 by – – Oldest known Earth rocksOldest known Earth rocks

Ancient atmosphere is neither oxidizing nor Ancient atmosphere is neither oxidizing nor reducingreducing Gasses: COGasses: CO22; N; N22; H; H22O vapor O vapor

Earth’s AgeEarth’s AgeLava FlowLava Flow

• 3.2 by3.2 by – – Earth coolsEarth cools as collisions & as collisions & volcanic activity subsidevolcanic activity subside Atmosphere formsAtmosphere forms from from out gassingout gassing from from

rocks & gas capturerocks & gas capture Oceans formOceans form from from condensation of Hcondensation of H22OO from from

cooling surface & comet capture cooling surface & comet capture

• 2.2 by2.2 by – – Earth has continents & oceans Earth has continents & oceans like todaylike today Ancient atmosphere is neither oxidizing nor Ancient atmosphere is neither oxidizing nor

reducingreducing Gasses: COGasses: CO22; N; N22; H; H22O vapor O vapor

Radioactive DatingRadioactive Dating

• # Protons # Protons (p(p++) – ) – constant for each constant for each elementelement Atomic numberAtomic number

Examples: C = 6; H = 1 Examples: C = 6; H = 1

• # Neutrons # Neutrons (n(n00) – ) – variable for each variable for each elementelement Atomic mass number Atomic mass number = #p= #p++ + #n + #n00

Examples: C may be Examples: C may be 1212C, C, 1313C, or C, or 1414C; H C; H may be may be 11H, H, 22H H ((deuteriumdeuterium)), or , or 33H H ((tritiumtritium))

Radioactive DatingRadioactive Dating

• Radioactive isotopesRadioactive isotopes – – radioisotopesradioisotopes Elements w/ unstable nuclei that undergo Elements w/ unstable nuclei that undergo

radioactive decayradioactive decay – particles are released– particles are released Half-lifeHalf-life

Length of time for ½ of any sample of a Length of time for ½ of any sample of a radioisotope to decayradioisotope to decay

Half-life can vary from a fraction of a second Half-life can vary from a fraction of a second to billions of yearsto billions of years

Used inUsed in absolute datingabsolute datingSpecific time of existence Specific time of existence

Dating with Index FossilsDating with Index Fossils

• Index fossilsIndex fossils Extinct wide-spread species whose fossils Extinct wide-spread species whose fossils

can be found all over the worldcan be found all over the world Usually marine organismsUsually marine organisms

Carried world wide on ocean currentsCarried world wide on ocean currents Used inUsed in relative datingrelative dating

Fossils of a species found & dated in one Fossils of a species found & dated in one region of the Earth are assumed to be the region of the Earth are assumed to be the same same relativerelative age as those of the same age as those of the same species found in another region species found in another region

Extinct Extinct brachiopodsbrachiopods

Experimental Synthesis: Experimental Synthesis: Organic CompoundsOrganic Compounds

• Miller-Urey Experiment Miller-Urey Experiment (1953)(1953)

Tested Oparin’s hypothesisTested Oparin’s hypothesisCirculated HCirculated H22O vapor & other gasses O vapor & other gasses

through chamber w/ electric sparking through chamber w/ electric sparking devicedevice

Condensed vapor into liquid water Condensed vapor into liquid water Analyzed condensate for organic Analyzed condensate for organic

compounds compounds

ResultsResultsSome amino acids & other organic Some amino acids & other organic

compounds formedcompounds formed

Miller-Urey ExperimentMiller-Urey Experiment


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Experimental Synthesis: Experimental Synthesis: Organic CompoundsOrganic Compounds

• Further Experiments Further Experiments (1960s-1980s)(1960s-1980s)

Tested Oparin’s hypothesisTested Oparin’s hypothesisUsed a variety of gassesUsed a variety of gassesUsed a variety of energy sources Used a variety of energy sources

ResultsResultsAll 20 amino acidsAll 20 amino acidsSimple mono- & di-saccharidesSimple mono- & di-saccharidesFatty acidsFatty acidsATPATPRNA & DNA nucleotidesRNA & DNA nucleotides

Modern StudiesModern StudiesSuggest Suggest Thermal VentsThermal Vents

• Further Experiments Further Experiments (1990s)(1990s)

Ancient atmosphere neither Ancient atmosphere neither reducingreducing nor nor oxidizingoxidizingGasses: COGasses: CO22; N; N22; H; H22O vapor O vapor Energy sources: hot minerals Energy sources: hot minerals

Synthesis of organicsSynthesis of organics – near undersea – near undersea erupting erupting volcanoesvolcanoes or or thermal ventsthermal ventsRich in Rich in sulfursulfur & & ironiron compounds compoundsReducing conditions Reducing conditions – H– H22SS

Life at Hydrothermal VentsLife at Hydrothermal Vents


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Organic Compounds Organic Compounds from Beyond Earthfrom Beyond Earth

• Organic compounds are abundant Organic compounds are abundant w/in our galaxyw/in our galaxy Form in giant dust clouds in spaceForm in giant dust clouds in space

• Organic compounds can be carried Organic compounds can be carried to earth by comets & meteorites to earth by comets & meteorites May have accumulated in oceans over May have accumulated in oceans over

millions of years during formation of millions of years during formation of the Earththe Earth

The First Organic The First Organic CompoundsCompounds• Oparin’s Hypothesis Oparin’s Hypothesis (1923)(1923)

Early Earth atmosphereEarly Earth atmosphereReducing gasses presentReducing gasses presentNHNH33 (ammonia)(ammonia); H; H22 (hydrogen gas)(hydrogen gas); H; H22O O (water vapor)(water vapor); ;

CHCH44 (methane)(methane) Energy source – lightning & UV radiation Energy source – lightning & UV radiation

• ScenarioScenario::– Simple organic compounds form in Simple organic compounds form in

atmosphereatmosphere– Compounds rained into oceansCompounds rained into oceans– Complex organic compounds form from Complex organic compounds form from

chemical reactions in presence of lightning & chemical reactions in presence of lightning & UV radiationUV radiation

From Molecules toFrom Molecules toCell-like StructuresCell-like Structures

• ProtobiontsProtobionts Form spontaneously in laboratory conditions Form spontaneously in laboratory conditions

from abiotically produced organic from abiotically produced organic compoundscompounds

Have some life-like propertiesHave some life-like propertiesReproduce by buddingReproduce by buddingExhibit metabolic abilityExhibit metabolic ability

• MicrospheresMicrospheres Proteins organized into a membraneProteins organized into a membrane

• CoacervatesCoacervates Linked amino acids & sugars organized into Linked amino acids & sugars organized into

a dropleta droplet

The First Life-formsThe First Life-forms

• The Origin of HeredityThe Origin of Heredity• The Roles of RNAThe Roles of RNA• The First ProkaryotesThe First Prokaryotes• The First EukaryotesThe First Eukaryotes


• TSW…TSW…1.1. Explain the importance of the chemistry of Explain the importance of the chemistry of

RNARNA in relation to the origin of life in relation to the origin of life2.2. List 3 inferred characteristics that describe List 3 inferred characteristics that describe

the the first forms of cellular lifefirst forms of cellular life on Earth on Earth3.3. Name 2 types of Name 2 types of autotrophyautotrophy & describe the & describe the

difference btw themdifference btw them4.4. Define Define endosymbiosisendosymbiosis, & explain why it is , & explain why it is

important in the history of eukaryotesimportant in the history of eukaryotes

HeredityHeredityReview:Review: TranscriptionTranscription && TranslationTranslation

• Heredity & PhenotypeHeredity & Phenotype DNADNA RNARNA PROTEINPROTEIN

Proteins give us our individual physical Proteins give us our individual physical appearance & physiology appearance & physiology

• Q.Q. Why is RNA necessary?Why is RNA necessary? DNA is also a templateDNA is also a template

Why not make proteins directly from DNA?Why not make proteins directly from DNA?

• A.A. It probably evolved 1stIt probably evolved 1st RNA is simpler & readily produced by aboitic RNA is simpler & readily produced by aboitic

processes processes Many viruses reproduce using RNAMany viruses reproduce using RNA

Origin of HeredityOrigin of HeredityBIG-TIME QUESTION!!!BIG-TIME QUESTION!!! Replication Replication requiresrequires a a hereditary hereditary substancesubstance. . AlsoAlso, replication , replication requires proteins to requires proteins to catalyze the catalyze the replication processreplication process..

Conundrum!!!Conundrum!!! ProteinsProteins cannot be formed w/out cannot be formed w/out nucleic acidsnucleic acids. . Mmmmm…but Mmmmm…but nucleic acids cannot be nucleic acids cannot be formed w/out proteins!formed w/out proteins!

Heredity & RNAHeredity & RNA

• Roles of RNARoles of RNA Transcription & translation (per earlier Transcription & translation (per earlier

chapter)chapter) RibozymeRibozyme –– RNA molecule RNA molecule::

Acts as an enzymeActs as an enzymeReplicates itselfReplicates itself

• The 1The 1stst life-form MAY have been a protobiont-like “cell” life-form MAY have been a protobiont-like “cell” w/ ribozyme-like RNA enclosed w/ ribozyme-like RNA enclosed It would contain a “It would contain a “genetic codegenetic code”” It could replicate its It could replicate its hereditary materialhereditary material It could It could evolveevolve via natural selection via natural selection It could catalyze the It could catalyze the synthesis of proteinssynthesis of proteins

What’s not to like?What’s not to like?

The First ProkaryotesThe First ProkaryotesSimilar to ArchaebacteriaSimilar to Archaebacteria

• Bacteria-like Organisms Bacteria-like Organisms (3.8+ by)(3.8+ by) Anaerobic metabolismAnaerobic metabolism

Did not use ODid not use O22

HeterotrophyHeterotrophyTook in organic molecules from the environmentTook in organic molecules from the environment

• Autotrophic LifeAutotrophic Life Chemoautotrophy Chemoautotrophy –– chemosynthesischemosynthesis

Use COUse CO2 2 as C sourceas C source (like photoautotrophy) (like photoautotrophy)

Use Use inorganic moleculesinorganic molecules (H (H22S) S) as energy sourceas energy source (not sunlight)(not sunlight)

Later Forms:Later Forms:

Bacteria & CyanobacteriaBacteria & Cyanobacteria• Cyanobacteria Cyanobacteria (3.8 by ?)(3.8 by ?)

PhotosynthesisPhotosynthesisUses COUses CO22 as C source as C source

Uses Uses sunlightsunlight as energy source as energy sourceProduces OProduces O22 as a byproduct: as a byproduct: “Oxygen Revolution”“Oxygen Revolution”

First fossils First fossils – 3.5 by– 3.5 byLook like modern cyanobacteriaLook like modern cyanobacteria

• Aerobic MetabolismAerobic Metabolism Evolved to absorb poisonous OEvolved to absorb poisonous O22 from from

photosynthesizing cellsphotosynthesizing cells Uses OUses O22 to “burn” sugar & produce ATP energy to “burn” sugar & produce ATP energy

StromatolitesStromatolites& Bacterial Mats& Bacterial Mats

The First EukaryotesThe First Eukaryotes

• Eukaryotes Eukaryotes (2 – 1.5 by)(2 – 1.5 by) EndosymbiosisEndosymbiosis

Small prokaryotes invade larger Small prokaryotes invade larger prokaryoteprokaryote

MutualismMutualism: symbiotic relationship begins: symbiotic relationship begins Membrane InfoldingMembrane Infolding

Regions of prokaryote cell membrane Regions of prokaryote cell membrane loop inward & pinch off into cell interiorloop inward & pinch off into cell interior

Membranes are metabolically dedicated Membranes are metabolically dedicated to specific tasksto specific tasks

The GeologicThe GeologicTime ScaleTime Scale

Time PeriodsTime Periods•EonsEons (ex. (ex. PhanerozoicPhanerozoic))

ErasEras (ex. (ex. CenozoicCenozoic)) PeriodsPeriods (ex. (ex. QuaternaryQuaternary))

•EpochEpoch (ex. (ex. HoloceneHolocene))

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Origin of Life Biogenesis Earth’s History The First Life-forms