Marks – Reading Quizzes and Assignments ● New marking scheme; grades in between NCR/CR, CR/CR+ ● Reading Quizes will be multiple choice, solely to make.

Marks – Reading Quizzes and AssignmentsMarks – Reading Quizzes and Assignments

● New marking scheme; grades in between New marking scheme; grades in between NCR/CR, CR/CR+NCR/CR, CR/CR+

● Reading Quizes will be multiple choice, solely to Reading Quizes will be multiple choice, solely to make sure material is readmake sure material is read

– Free points if you've done the readingFree points if you've done the reading● Reading Quiz:Reading Quiz:

– 0 NCR, 3 NCR+, 2 CR, 6 CR+, 1 CR++0 NCR, 3 NCR+, 2 CR, 6 CR+, 1 CR++● Assignments:Assignments:

– 0 NCR, 0 NCR+, 4 CR, 9 CR+, 1 CR++0 NCR, 0 NCR+, 4 CR, 9 CR+, 1 CR++

Summary of last class: Stellar cycleSummary of last class: Stellar cycle

Summary of Last ClassSummary of Last Class● Stars form in turbulent gas cloudsStars form in turbulent gas clouds● Dense regions begin to collapse, heat up, spin upDense regions begin to collapse, heat up, spin up● Disks formDisks form

– Planet formationPlanet formation● If massive enough, nuclear burning begins in coreIf massive enough, nuclear burning begins in core● Very massive stars burn very fast; more modest stars Very massive stars burn very fast; more modest stars

(the Sun) burn over billions of years; smaller stars (the Sun) burn over billions of years; smaller stars slower stillslower still

● Smaller stars eject some of their mass leaving behind Smaller stars eject some of their mass leaving behind a white dwarfa white dwarf

● Larger stars blow up completely, ejecting almost all Larger stars blow up completely, ejecting almost all heavy elements into gas clouds for next stage of star heavy elements into gas clouds for next stage of star formationformation

Feedback:Feedback:● Most unclear item from last week's readings?Most unclear item from last week's readings?

What we're going to cover todayWhat we're going to cover today● Earths BiochemistryEarths Biochemistry

– Building blocks for complex chemistryBuilding blocks for complex chemistry– Amino acids -> proteins, nucleotides -> DNAAmino acids -> proteins, nucleotides -> DNA– EvolutionEvolution

● Early life on EarthEarly life on Earth

– Life <-> AtmosphereLife <-> Atmosphere– Chemical origin of lifeChemical origin of life– ProtocellsProtocells– Miller-UreyMiller-Urey

Earth's BiochemistryEarth's Biochemistry

● Abundance of ElementsAbundance of Elements● Building blocks of biochemistryBuilding blocks of biochemistry● PolymersPolymers● ProteinsProteins● Amino AcidsAmino Acids● DNA/RNADNA/RNA● Nucleic AcidsNucleic Acids● ReproductionReproduction● GenesGenes● Expression of GenesExpression of Genes

Abundance of ElementsAbundance of Elements● Hydrogen and Helium most Hydrogen and Helium most

abundant in Universe (from abundant in Universe (from Big Bang)Big Bang)

● Not most abundant on rocky Not most abundant on rocky planets – evaporationplanets – evaporation

● Heavy elements produced in Heavy elements produced in stars, and will follow similar stars, and will follow similar overall patternoverall pattern

● Systems that have material Systems that have material processed by more stars will processed by more stars will have overall more heavy have overall more heavy elements compared to H, He.elements compared to H, He.

CarbonCarbon

● Of the commonly occurring heavy Of the commonly occurring heavy elements, Carbon can form the basis elements, Carbon can form the basis for very complex moleculesfor very complex molecules

● Complex molecules can interact with Complex molecules can interact with each other in more varied wayseach other in more varied ways

● More complex interactions -> more More complex interactions -> more pathways for life to beginpathways for life to begin

SiliconSilicon

● PlentifulPlentiful● Similar to Carbon (can form Similar to Carbon (can form

4 bonds)4 bonds)● Tends to react with oxygen Tends to react with oxygen

to form simple crystalline to form simple crystalline structures - `silicates'structures - `silicates'

● Rocks, SandRocks, Sand● Silicon good for making Silicon good for making

computers; not so good for computers; not so good for making entire living making entire living organisms.organisms.

OxygenOxygen● PlentifulPlentiful● Can only form two bondsCan only form two bonds● VERY REACTIVEVERY REACTIVE

– Makes stuff burn,Makes stuff burn,– rust...rust...

● Good for extracting energy in Good for extracting energy in organisms organisms if controlledif controlled

● Very little free oxygen on early Very little free oxygen on early earthearth

● For early organisms, Oxygen was For early organisms, Oxygen was a poisonous pollutanta poisonous pollutant

WaterWater● `Polar': + and – charges`Polar': + and – charges● Molecules attracted to each otherMolecules attracted to each other

– Water Water expandsexpands when freezes when freezes– Very high boiling pointVery high boiling point

● Very active:Very active:

– Other polar molecules attracted Other polar molecules attracted to water/dissolve in it easily to water/dissolve in it easily (hydrophilic/water-soluble)(hydrophilic/water-soluble)

– Non-polar molecules repelled, Non-polar molecules repelled, don't dissolve (hydrophobic) don't dissolve (hydrophobic)

+ +

-

Building Blocks of LifeBuilding Blocks of Life● These machinery of life is made of polymers These machinery of life is made of polymers

– Built out of chains of simpler molecules Built out of chains of simpler molecules (monomers)(monomers)

– `modular'`modular'● Three important polymers in Earth's biology:Three important polymers in Earth's biology:

– ProteinsProteins● Building blocks for everythingBuilding blocks for everything

– DNADNA● Repository of genetic informationRepository of genetic information

– RNARNA● Takes information from DNA, builds proteinsTakes information from DNA, builds proteins

Scale: Needle, Salt Grain (~5x mag)Scale: Needle, Salt Grain (~5x mag)

Scale: Cells (~ 100x mag)Scale: Cells (~ 100x mag)

Grain of Salt

Human Hair

Amoeba

Paramecium Human Egg

Scale: Cells (~ 1000x mag)Scale: Cells (~ 1000x mag)Human Egg

E. Coli

Bakers Yeast

Red Blood Cells

Scale: Cells + Viruses (~ 100,000x mag)Scale: Cells + Viruses (~ 100,000x mag)

E. ColiBacteriophage

HIV

DNA strand

Tobacco Mosaic virus

Molecules (~ 1,000,000x mag)Molecules (~ 1,000,000x mag)

Strand of Bacterial DNA Glucose

Hemoglobin

Things are Very Different when Things are Very Different when you're a Moleculeyou're a Molecule

● Gravity is not so importantGravity is not so important● Electrical, molecular forces areElectrical, molecular forces are● WATERWATER

– Constantly jostled by water moleculesConstantly jostled by water molecules– Some parts of molecules attracted to water Some parts of molecules attracted to water

(hydrophilic)(hydrophilic)– Some parts repelled (hydrophobic)Some parts repelled (hydrophobic)

● Molecules behave like little machines that are Molecules behave like little machines that are pushed around by electrical forcespushed around by electrical forces

ProteinsProteins

● Proteins are long strings of Proteins are long strings of amino acidsamino acids

● The strings fold into The strings fold into complex shapes as they formcomplex shapes as they form

– Buffeted by waterBuffeted by water– Bonds linking one part Bonds linking one part

of chain to the otherof chain to the other

ProteinsProteins● A protein's A protein's functionfunction is is

determined by it's shape or determined by it's shape or structurestructure..

● It's structure is determined by the It's structure is determined by the amino acids its made up ofamino acids its made up of

● Enzymes are proteins which Enzymes are proteins which speed up certain reactionsspeed up certain reactions

● Maltase breaks maltose down Maltase breaks maltose down into two glucose moleculesinto two glucose molecules

● Maltose fits into `active site' Maltose fits into `active site' ● Lock-and-keyLock-and-key● E. Coli E. Coli has ~1000 different has ~1000 different

proteinsproteins

Amino AcidsAmino Acids

● Building blocks of proteinsBuilding blocks of proteins● Twenty of them occur in Earth's Twenty of them occur in Earth's

biologybiology● Simple molecules: 13 – 27 atomsSimple molecules: 13 – 27 atoms● Carbon, Hydrogen, Oxygen, Carbon, Hydrogen, Oxygen,

Nitrogen; two also have SulfurNitrogen; two also have Sulfur● Chemically identical mirror images Chemically identical mirror images

of these compounds (right-handed of these compounds (right-handed versions) do not occur in Earth's versions) do not occur in Earth's biologybiology

● Typical protein might be built of Typical protein might be built of ~100 amino acids~100 amino acids

alanine

tyrosine

Amino AcidsAmino Acids

● Amino acid consists of:Amino acid consists of:

– NHNH33 group (amine) group (amine)

– COOH group (acid)COOH group (acid)– Connected by a Carbon which also Connected by a Carbon which also

connects to a side chainconnects to a side chain– It's the properties of the side chain It's the properties of the side chain

which differentiate the amino acidswhich differentiate the amino acids– 5 are hydrophobic, 7 hydrophilic, 8 5 are hydrophobic, 7 hydrophilic, 8

are water-neutralare water-neutral

Amino AcidsAmino Acids

● The COOH end of one amino acid links The COOH end of one amino acid links up with the NHup with the NH

33 group of the next group of the next

– Bond called `peptide bond'Bond called `peptide bond'– Water releasedWater released

● ``polypeptides''``polypeptides''● Side chains are on alternate sides of the Side chains are on alternate sides of the

chainchain● In principle, uncountably vast numbers of In principle, uncountably vast numbers of

proteins are possibleproteins are possible● In practice, most organisms make/use In practice, most organisms make/use

fewer than 10,000fewer than 10,000

Nucleic AcidsNucleic Acids

● Proteins are encoded in a cell's Proteins are encoded in a cell's DNA, and built on a `scaffold' of DNA, and built on a `scaffold' of RNA.RNA.

● RNA and DNA are both polymers RNA and DNA are both polymers of nucleotides – molecules with of nucleotides – molecules with bases as shown herebases as shown here

● Both DNA and RNA have an Both DNA and RNA have an `alphabet' of 4 bases`alphabet' of 4 bases

(DNA only)(RNA only)

NucleotidesNucleotides

● These bases attach to a sugar and These bases attach to a sugar and phosphate to form nucleotidesphosphate to form nucleotides

● These nucleotides are the These nucleotides are the monomers that make up DNA, monomers that make up DNA, RNARNA

● Sugar, phosphate makes up the Sugar, phosphate makes up the backbone of the structure, with the backbone of the structure, with the base sticking outbase sticking out

DNADNA

● A strand of DNA contains a long A strand of DNA contains a long series of nucleotides, in a series series of nucleotides, in a series of genes (AAGCTC...)of genes (AAGCTC...)

● Each gene is separated by a stop Each gene is separated by a stop signalsignal

● Contains all the information for Contains all the information for making all the proteins in the cellmaking all the proteins in the cell

DNADNA● Proteins are made when an Proteins are made when an

enzyme walks long the DNA enzyme walks long the DNA strand, transcribing it into an strand, transcribing it into an RNA strandRNA strand

● The RNA strand then gets The RNA strand then gets translated into a protein.translated into a protein.

– Each 3 `letter' sequence gets Each 3 `letter' sequence gets translated into a single translated into a single amino acidamino acid

– 64 possible 3-letter 64 possible 3-letter sequences; 20 amino acidssequences; 20 amino acids

– Some acids have several Some acids have several translationstranslations

DNADNA● DNA strands come in DNA strands come in

interwoven pairs.interwoven pairs.● Each pair is linked up at every Each pair is linked up at every

basebase● Each base with link up with Each base with link up with

only one other base;only one other base;

– (U/T) with A(U/T) with A– C with G C with G

● Both strands have Both strands have complementary informationcomplementary information

ReproductionReproduction

● This `interwoven complementary This `interwoven complementary pair' makes replication fairly pair' makes replication fairly straightforwardstraightforward

● Enzymes can march along the Enzymes can march along the strand, separating it in twostrand, separating it in two

● Each strand can then be matched up Each strand can then be matched up with the corresponding nucleotides, with the corresponding nucleotides, and rebuild its second halfand rebuild its second half

● One twisted pair becomes two, One twisted pair becomes two, containing same informationcontaining same information

Mutation and EvolutionMutation and Evolution● ``The capacity to blunder slightly is ``The capacity to blunder slightly is

the real marvel of DNA. Without the real marvel of DNA. Without this special attribute, we would still this special attribute, we would still be anaerobic bacteria, and there be anaerobic bacteria, and there would be no music.'' -- Lewis would be no music.'' -- Lewis Thomas, Thomas, The Medusa and the SnailThe Medusa and the Snail

● Replication does not always occur Replication does not always occur perfectlyperfectly

● DNA can be damaged, or `typos' can DNA can be damaged, or `typos' can occur during copyingoccur during copying

● Mutation of single cell usually has Mutation of single cell usually has no effect. But mutation in a sex cell no effect. But mutation in a sex cell will cause mutation in offspringwill cause mutation in offspring

Mutation and EvolutionMutation and Evolution

● Some of these mutations have no Some of these mutations have no effect at alleffect at all

● Of those that do, the vast majority Of those that do, the vast majority are extremely damaging and kill are extremely damaging and kill offspring - doesn't propagate offspring - doesn't propagate

● Some are fairly neutral (or have Some are fairly neutral (or have good+bad consequences) and will good+bad consequences) and will persist in future generationspersist in future generations

● Some are so positive that greatly Some are so positive that greatly helps survivability/reproduction, and helps survivability/reproduction, and soon propagates through much of soon propagates through much of speciesspecies

Diversity and AdaptabilityDiversity and Adaptability

● Having a wide range of neutral mutations is greatly Having a wide range of neutral mutations is greatly advantageous for species survivabilityadvantageous for species survivability

● If new danger occurs (predator, disease), better If new danger occurs (predator, disease), better chance that some in the population will have chance chance that some in the population will have chance of survivalof survival

● Danger of mono culturesDanger of mono cultures

Origin of Life On EarthOrigin of Life On Earth

● Earth's FormationEarth's Formation● AtmosphereAtmosphere● Evolution of AtmosphereEvolution of Atmosphere● Life and the AtmosphereLife and the Atmosphere● Chemical modelChemical model● Primordial SoupPrimordial Soup● Miller-UreyMiller-Urey● Other AlternativesOther Alternatives● PolymerizationPolymerization● Beginnings of lifeBeginnings of life

Earth's FormationEarth's Formation

● Condensed out of solar diskCondensed out of solar disk● Small pieces (planetesimals) merging togetherSmall pieces (planetesimals) merging together● Very hot – radioactive materials, collisionsVery hot – radioactive materials, collisions● Ultraviolet radiation from sun (no protecting Ultraviolet radiation from sun (no protecting

ozone)ozone)

– PhotodissociationPhotodissociation● Crust takes a long time to formCrust takes a long time to form● Very geothermally activeVery geothermally active

AtmosphereAtmosphere● Probably never had an atmosphere that formed Probably never had an atmosphere that formed

with the planet; planetsimals too small to capture with the planet; planetsimals too small to capture atmosphereatmosphere

● As Earth becomes massive enough to trap gases, As Earth becomes massive enough to trap gases, atmosphere forms as colliding objects (late-atmosphere forms as colliding objects (late-accreting material) are vaporized accreting material) are vaporized

● Volatile elements (lightest and easiest to Volatile elements (lightest and easiest to vaporize) can most easily diffuse awayvaporize) can most easily diffuse away

– Hydrogen, carbon, nitrogen, oxygenHydrogen, carbon, nitrogen, oxygen● Free hydrogen most easily evaporatedFree hydrogen most easily evaporated● Photodissociation breaks up moleculesPhotodissociation breaks up molecules

Evolution of AtmosphereEvolution of Atmosphere

● As hydrogen leaves, ozone can formAs hydrogen leaves, ozone can form

– Less hydrogen to suck up free oxygen into Less hydrogen to suck up free oxygen into waterwater

● Cuts down ultraviolet light, photodissociationCuts down ultraviolet light, photodissociation● Atmosphere begins to stabilizeAtmosphere begins to stabilize

– Water vaporWater vapor– Carbon Dioxide Carbon Dioxide – NitrogenNitrogen– Carbon MonoxideCarbon Monoxide– Very little OxygenVery little Oxygen– Even less OzoneEven less Ozone

Evolution of Atmosphere: COEvolution of Atmosphere: CO22

● Most atmospheric gases easily dissolved in waterMost atmospheric gases easily dissolved in water● Gases easily exchanged between oceans and Gases easily exchanged between oceans and

atmosphereatmosphere

● COCO22 in water can form calcium carbonate (limestone, in water can form calcium carbonate (limestone,

chalk)chalk)

● COCO22 tends to get sucked out of the atmosphere tends to get sucked out of the atmosphere

● Can be released by volcanoes, eroding rocks, decay Can be released by volcanoes, eroding rocks, decay of more complex chemicals, and lifeof more complex chemicals, and life

Evolution of AtmosphereEvolution of Atmosphere

● Nitrogen:Nitrogen:

– Released from subsurface rock into Released from subsurface rock into atmosphere through vents -- `outgassing'atmosphere through vents -- `outgassing'

● Argon:Argon:

– Inert gas; does not willingly interact with Inert gas; does not willingly interact with other elementsother elements

– Mostly comes from decay of radioactive Mostly comes from decay of radioactive potassium on Earth's crust and from below potassium on Earth's crust and from below

– `Outgassed'`Outgassed'– Of limited importance because of its inert Of limited importance because of its inert

naturenature

Evolution of Atmosphere: ArgonEvolution of Atmosphere: Argon

● Inert gas; does not willingly interact with other Inert gas; does not willingly interact with other elementselements

● Mostly comes from decay of radioactive Mostly comes from decay of radioactive potassium on Earth's crust and from below potassium on Earth's crust and from below

● `Outgassed' through volcanic vents, etc.`Outgassed' through volcanic vents, etc.● Significant trace quantities in modern Significant trace quantities in modern

atmosphere (~1%)atmosphere (~1%)● Of limited importance because of its inert natureOf limited importance because of its inert nature

Origin of Life: Chemical modelOrigin of Life: Chemical model

● Very difficult for compounds essential for life Very difficult for compounds essential for life (amino or nucleic acids) to form in the presence (amino or nucleic acids) to form in the presence of free Oxygenof free Oxygen

● Oxygen is so reactive it immediately reduces any Oxygen is so reactive it immediately reduces any forming organic compounds to carbon dioxide, forming organic compounds to carbon dioxide, etc.etc.

● Earliest rocks (2.5 billion years or longer ago) Earliest rocks (2.5 billion years or longer ago) appear to have formed in low-Oxygen appear to have formed in low-Oxygen environments.environments.

● If life had to form on Earth today, very difficult If life had to form on Earth today, very difficult to see how it would happen.to see how it would happen.

Origin of Life: Chemical modelOrigin of Life: Chemical model

● Absent Oxygen, possible for building blocks to Absent Oxygen, possible for building blocks to form spontaneously via chemical reactionsform spontaneously via chemical reactions

● Energy is available:Energy is available:

– Geothermal (underwater volcanic vents)Geothermal (underwater volcanic vents)– Solar (light, ultraviolet)Solar (light, ultraviolet)– Electrical (lightning)Electrical (lightning)

● All the elements are available in atmosphere, on All the elements are available in atmosphere, on surface, in oceanssurface, in oceans

Primordial SoupPrimordial Soup

● Refers to the early mix of chemicals in the Refers to the early mix of chemicals in the atmosphere and oceansatmosphere and oceans

● Lots of dissolved raw ingredients in oceans, Lots of dissolved raw ingredients in oceans, atmosphereatmosphere

● Oceans more plausible:Oceans more plausible:

– Higher density, easier for reactions to Higher density, easier for reactions to occuroccur

– Most creatures have abundances of Most creatures have abundances of elements similar to oceanselements similar to oceans

● Something needs to occur for reactions to occurSomething needs to occur for reactions to occur

Miller-Urey ExperimentMiller-Urey Experiment

● 1953 here in Chicago1953 here in Chicago● Simulates oceans and Simulates oceans and

atmosphere of a young atmosphere of a young EarthEarth

● Ammonia, methane, Ammonia, methane, hydrogen in atmospherehydrogen in atmosphere

● After only a few days, After only a few days, two amino acids and the two amino acids and the nucleotide bases have nucleotide bases have formed!formed!

Miller-Urey ExperimentMiller-Urey Experiment

Miller-Urey ExperimentMiller-Urey Experiment

● Atmosphere is not realisticAtmosphere is not realistic● Far too much hydrogenFar too much hydrogen● In 1950s, simpler theories of planet In 1950s, simpler theories of planet

formation; planet formed all at once, with formation; planet formed all at once, with atmosphere from solar nebulaatmosphere from solar nebula

● Almost certainly didn't happen that wayAlmost certainly didn't happen that way● Far less Hydrogen in atmosphere than Miller-Far less Hydrogen in atmosphere than Miller-

Urey Experiment suggestedUrey Experiment suggested

Miller-Urey ExperimentMiller-Urey Experiment

● Useless? No!Useless? No!● With that much hydrogen in atmosphere, With that much hydrogen in atmosphere,

within only a few days formed a bunch of within only a few days formed a bunch of important compoundsimportant compounds

● With much less hydrogen its much harderWith much less hydrogen its much harder● Early Earth had millions of yearsEarly Earth had millions of years● Very suggestive that this is the right track, Very suggestive that this is the right track,

but need to experimentally verify that still but need to experimentally verify that still feasible in lower-hydrogen atmospherefeasible in lower-hydrogen atmosphere

● Amino acids are also found in meteorites... Amino acids are also found in meteorites...

Other AlternativesOther Alternatives

● Amino acids from space?Amino acids from space?● Meteor impact w/ amino acidsMeteor impact w/ amino acids

– Causes craterCauses crater– Pools with waterPools with water– Breakdown of other organics provides Breakdown of other organics provides

hydrogenhydrogen– Back to Miller-UreyBack to Miller-Urey

● OrOr

– Whatever process produces amino acids in Whatever process produces amino acids in molecular clouds/meteors also at play on molecular clouds/meteors also at play on early Earthearly Earth

PolymerizationPolymerization

● One way or another, can seem to form amino or One way or another, can seem to form amino or nucleic acidsnucleic acids

● Even if it requires a fairly rare event, over Even if it requires a fairly rare event, over hundreds of millions of years and an entire hundreds of millions of years and an entire planet, a lot of rare things can happenplanet, a lot of rare things can happen

● How to form the polymers --- protein or How to form the polymers --- protein or DNA/RNA?DNA/RNA?

● In our biology, enzymes build proteins out of In our biology, enzymes build proteins out of amino acids or DNA/RNA out of nucleotidesamino acids or DNA/RNA out of nucleotides

● But these enzymes are themselves proteins.But these enzymes are themselves proteins.

PolymerizationPolymerization

● No good answer to this question yetNo good answer to this question yet● Best lead so far:Best lead so far:

– Can also build `RNA-enzymes'Can also build `RNA-enzymes'– If can get a bit of RNA to form from If can get a bit of RNA to form from

nucleotides, can self-catalyze, building nucleotides, can self-catalyze, building moremore

● Have to get the RNA to form in first placeHave to get the RNA to form in first place● Clay grain may allow polymerization the same Clay grain may allow polymerization the same

way dust grains in molecular clouds allow for way dust grains in molecular clouds allow for molecule formationmolecule formation

PolymerizationPolymerization

● May be `missing link'; some previous life form May be `missing link'; some previous life form that was based on something simpler and helped that was based on something simpler and helped form polymersform polymers

● But if it existed, where did it go? Successful life But if it existed, where did it go? Successful life forms tend to stayforms tend to stay

● Blue-green algae has existed for 3 billion years Blue-green algae has existed for 3 billion years essentially unchangedessentially unchanged

● Perhaps couldn't survive oxygen in atmospherePerhaps couldn't survive oxygen in atmosphere

Beginnings of lifeBeginnings of life● Once polymers form, process speeds upOnce polymers form, process speeds up● Proteins can act on other proteins, and on Proteins can act on other proteins, and on

RNA/DNA.RNA/DNA.● RNA can act on Proteins, RNA, DNARNA can act on Proteins, RNA, DNA● New proteins, RNA, DNA constantly being New proteins, RNA, DNA constantly being

created, acted on, editedcreated, acted on, edited● As soon as some combination of molecules is As soon as some combination of molecules is

created that can self-replicate, there's an created that can self-replicate, there's an explosionexplosion

● `Chemical evolution' takes over`Chemical evolution' takes over● Chemical systems can get more and more Chemical systems can get more and more

complicatedcomplicated

Beginnings of lifeBeginnings of life● Once polymers form, process speeds upOnce polymers form, process speeds up● Proteins can act on other proteins, and on Proteins can act on other proteins, and on

RNA/DNA.RNA/DNA.● RNA can act on Proteins, RNA, DNARNA can act on Proteins, RNA, DNA● New proteins, RNA, DNA constantly being New proteins, RNA, DNA constantly being

created, acted on, editedcreated, acted on, edited● As soon as some combination of molecules is As soon as some combination of molecules is

created that can self-replicate, there's an created that can self-replicate, there's an explosionexplosion

● `Chemical evolution' takes over`Chemical evolution' takes over● Chemical systems can get more and more Chemical systems can get more and more

complicatedcomplicated

Life and the AtmosphereLife and the Atmosphere● Rocks that formed 2.5 billion years ago did so in Rocks that formed 2.5 billion years ago did so in

very oxygen-poor conditionsvery oxygen-poor conditions● Microscopic fossils -> life was certainly present Microscopic fossils -> life was certainly present

~3 billion years ago~3 billion years ago● For at least 500 million years, life existed For at least 500 million years, life existed

without significant oxygen in atmospherewithout significant oxygen in atmosphere● `blue-green algae' (cyanobacteria)`blue-green algae' (cyanobacteria)

– Single-celled prokaroyotesSingle-celled prokaroyotes– Anaerobic bacteriaAnaerobic bacteria

● Single-handedly modified atmosphere by Single-handedly modified atmosphere by `exhaling' enough Oxygen to allow Oxygen-`exhaling' enough Oxygen to allow Oxygen-breathers to begin to evolvebreathers to begin to evolve

Life and the AtmosphereLife and the Atmosphere● Life begins processing NitrogenLife begins processing Nitrogen

– Some bacteria `fix' Nitrogen into soilSome bacteria `fix' Nitrogen into soil– Some plants release Nitrogen into Some plants release Nitrogen into

atmosphereatmosphere● Newly formed Oxygen reacts with all Carbon Newly formed Oxygen reacts with all Carbon

Monoxide in atmosphere to form COMonoxide in atmosphere to form CO22

● Large amount of Oxygen, absence of Carbon Large amount of Oxygen, absence of Carbon Monoxide in atmospheres of extra-solar planets Monoxide in atmospheres of extra-solar planets could be a sign of life.could be a sign of life.

SummarySummary● ``Big Picture'' fairly clear; details murky``Big Picture'' fairly clear; details murky● 4.5 Gyr ago, Earth forms. Atmosphere contains 4.5 Gyr ago, Earth forms. Atmosphere contains

Carbon, Nitrogen, some small hydrogen, no Carbon, Nitrogen, some small hydrogen, no Oxygen; comes from impacts, outgassingOxygen; comes from impacts, outgassing

● Primordial soup of organic compounds and Primordial soup of organic compounds and phosphates form over few hundred million years phosphates form over few hundred million years from raw ingredients and abundant energy from raw ingredients and abundant energy sourcessources

● Continuing chemical reactions give amino acids, Continuing chemical reactions give amino acids, nucleotidesnucleotides

● Polymers of these form on surfaces of clays (?)Polymers of these form on surfaces of clays (?)● Polymers act on each other, creating complex Polymers act on each other, creating complex

interacting systems; complexity grows.interacting systems; complexity grows.

Reading for Next WeekReading for Next Week

● Chapter 9 – evolution of intelligent life on earthChapter 9 – evolution of intelligent life on earth

– Going from simple biochemistry to simple Going from simple biochemistry to simple life, then complex lifelife, then complex life

– Eukariotic life and cell functioningEukariotic life and cell functioning– Reproduction and genesReproduction and genes– Multicellular lifeMulticellular life– Development of intelligent lifeDevelopment of intelligent life– Future evolution and co-evolutionFuture evolution and co-evolution