End-of-Term ProjectsEnd-of-Term Projects

● In class, May 14In class, May 14thth for both presentations and for both presentations and reportsreports

● Reports:Reports:

– ~12 pp on material which is relevant to ~12 pp on material which is relevant to coursecourse

● Presentations:Presentations:

– ~20min, hand in a ~1p summary~20min, hand in a ~1p summary● Worth 10 pts (5 assignments)Worth 10 pts (5 assignments)● Grades due May 17Grades due May 17thth; NOTHING ACCEPTED ; NOTHING ACCEPTED

after class time on 14after class time on 14thth..● Can pick up marked copies from my mailboxCan pick up marked copies from my mailbox

Search for Life In the Universe: `Best Of' Search for Life In the Universe: `Best Of' Edition. Edition.

● Clip Show #1: The Science behind the SearchClip Show #1: The Science behind the Search

Science in a NutshellScience in a Nutshell

Observations (reality)Observations (reality)

ExplanationExplanation(theory)(theory)

ConsequencesConsequences(predictions)(predictions)

TestsTests

Science in a NutshellScience in a Nutshell

● The universe is understandableThe universe is understandable● Scientific knowledge is foreverScientific knowledge is forever● Scientific ideas are subject to changeScientific ideas are subject to change● Science demands evidenceScience demands evidence● Science explains Science explains andand predicts predicts

Careful ObservationCareful Observation

● Careful observation is the beginnings of all Careful observation is the beginnings of all science.science.

● Observations can be of the world as it is or of Observations can be of the world as it is or of carefully set up situations to see what happens carefully set up situations to see what happens (experiments)(experiments)

● In some sciences experimentation isn't possible In some sciences experimentation isn't possible (astronomy) or is limited (human behavior), and (astronomy) or is limited (human behavior), and only observations are feasibleonly observations are feasible

● Making careful observations isn't as easy as it Making careful observations isn't as easy as it may seem.may seem.

Overthrow-ability of TheoriesOverthrow-ability of Theories

● Theories can be disproven by finding evidence Theories can be disproven by finding evidence which contrdicts them.which contrdicts them.

● (Evidence itself must be verified; data might be (Evidence itself must be verified; data might be wrong)wrong)

● Any new theory must explain everything that Any new theory must explain everything that previous theory did, plus the new evidence.previous theory did, plus the new evidence.

Complexity in LifeComplexity in Life

● Even the simplest life form has a lot more going Even the simplest life form has a lot more going on than even fairly complex non-alive thingson than even fairly complex non-alive things

Chemistry of LifeChemistry of Life

● Chemistry has as building blocks the elements Chemistry has as building blocks the elements around us.around us.

● Big bang: produced mainly Hydrogen, HeliumBig bang: produced mainly Hydrogen, Helium● Sun: Everything's Hydrogen, Helium, Oxygen, Sun: Everything's Hydrogen, Helium, Oxygen,

Carbon, small traces of other stuff – Pop I starCarbon, small traces of other stuff – Pop I star● Earth: Richer in heavier stuff (Iron, Silicon,...)Earth: Richer in heavier stuff (Iron, Silicon,...)● Other stars, planets likely to be similarOther stars, planets likely to be similar● Relative abundances of (Hydrogen, Helium) and Relative abundances of (Hydrogen, Helium) and

(Carbon, Oxygen, Silicon, Iron...) may vary (Carbon, Oxygen, Silicon, Iron...) may vary ● Of these building blocks, what chemicals can Of these building blocks, what chemicals can

build complex chemistry?build complex chemistry?

Chemistry of life: CarbonChemistry of life: Carbon

● Of plentiful stuff, Carbon (alone) can build very Of plentiful stuff, Carbon (alone) can build very complex moleculescomplex molecules

Chemistry of life: Water?Chemistry of life: Water?

● Water is essential to life on earthWater is essential to life on earth● Thought that life began in the water (more on Thought that life began in the water (more on

that in later lectures)that in later lectures)● For chemical life, need a way to get chemicals to For chemical life, need a way to get chemicals to

different part of the bodydifferent part of the body● Water is a very powerful solvent.Water is a very powerful solvent.

– Dissolve chemicalDissolve chemical– Allow transport through body in liquid Allow transport through body in liquid

formform● Very few liquid solvents as powerful, or as Very few liquid solvents as powerful, or as

common. common.

Limitations of waterLimitations of water

● If life depends on water, then very strict limit on If life depends on water, then very strict limit on where life can bewhere life can be

● Can't be anywhere colder than freezingCan't be anywhere colder than freezing● Can't be anywhere hotter than boilingCan't be anywhere hotter than boiling● Other liquid solvents have different Other liquid solvents have different

freezing/boiling points, but problem remainsfreezing/boiling points, but problem remains● Hard to see how chemicals can be efficiently Hard to see how chemicals can be efficiently

transported through a body otherwisetransported through a body otherwise

Water On MarsWater On Mars

● Current Mars rover saw Current Mars rover saw `spherules' (`blueberries') in `spherules' (`blueberries') in many places many places

● Could indicate waterCould indicate water

– Form as `concretions'Form as `concretions'– Speck of something in Speck of something in

waterwater– Other sediments build upOther sediments build up– Same process as pearls, Same process as pearls,

snowflakes, raindropssnowflakes, raindrops● But other possibilitiesBut other possibilities

Water On MarsWater On Mars

● Other evidence: rock Other evidence: rock formationsformations

● Suggestive of water erosionSuggestive of water erosion● In particular, spherule formed In particular, spherule formed

inside crack in rockinside crack in rock● Evidence that spherule did Evidence that spherule did

form through concretionform through concretion● Cracks seem to be from water Cracks seem to be from water

rivuletsrivulets

Water On MarsWater On Mars

● More evidence; build up of More evidence; build up of sulfates, other salts on surfacesulfates, other salts on surface

● Very strong evidence that Very strong evidence that water laced with minerals was water laced with minerals was flowingflowing

● When evaporated, left these When evaporated, left these minerals behindminerals behind

Water On MarsWater On Mars

● No evidence yet of lifeNo evidence yet of life● Water would seem to be a Water would seem to be a

necessary ingredientnecessary ingredient● No evidence for oceans, or No evidence for oceans, or

that Mars was warm enough that Mars was warm enough to have liquid water for long to have liquid water for long timetime

What sort of life are we interested in?What sort of life are we interested in?

● In our own solar system, even bacteria fossils In our own solar system, even bacteria fossils would be enormous find.would be enormous find.

● Have some chance of looking at Mars, other Have some chance of looking at Mars, other nearby planetsnearby planets

● For life outside our solar system, won't be able to For life outside our solar system, won't be able to visit for foreseeable futurevisit for foreseeable future

● Only way to recognize life is to receive signalsOnly way to recognize life is to receive signals● Life must be intelligent enough to communicate Life must be intelligent enough to communicate

with us in a way we can recognizewith us in a way we can recognize

The Distance LadderThe Distance Ladder● Four `realms' of Four `realms' of

distance in exploring distance in exploring UniverseUniverse

– Solar systemSolar system– Nearby starsNearby stars– Galactic distancesGalactic distances– Intergalactic Intergalactic

distancedistance● So vastly different that So vastly different that

each needs different each needs different techniques, units to techniques, units to measure distancesmeasure distances

Solar SystemSolar System

● Can use direct observation, simple Can use direct observation, simple geometry to measure solar system geometry to measure solar system distances to reasonable accuracydistances to reasonable accuracy

● These were available to the ancientsThese were available to the ancients● More modern techniques (radar, More modern techniques (radar,

spacecraft..) allow increased spacecraft..) allow increased accuracyaccuracy

New length unit: Astronomical Unit New length unit: Astronomical Unit (AU):(AU):

● Earth-Sun distance so handy for measuring solar Earth-Sun distance so handy for measuring solar system distances that new unit created:system distances that new unit created:

● 1 AU = mean distance between Earth and Sun1 AU = mean distance between Earth and Sun● 1 AU = 92,955,807 miles1 AU = 92,955,807 miles● Can use this information to work way up to next Can use this information to work way up to next

realm: nearby starsrealm: nearby stars

Paralaxes can be observed in starsParalaxes can be observed in stars

Paralaxes can be observed in starsParalaxes can be observed in stars

The displacement is measured as an The displacement is measured as an angle on the skyangle on the sky

● 0.5 degree: about your thumb at arms length0.5 degree: about your thumb at arms length● 1 arc minute: 1/601 arc minute: 1/60thth of a degree of a degree● 1 arc second: 1/601 arc second: 1/60thth of an arc minute of an arc minute● A distance at which the parallax (from Jan to A distance at which the parallax (from Jan to

Mar) is 1 arc second is a parsec (PARallax Mar) is 1 arc second is a parsec (PARallax SECond)SECond)

● Can find it from 1 AU with some trigCan find it from 1 AU with some trig● 1 pc = 206265 AU1 pc = 206265 AU

Distances to distant clusters of starsDistances to distant clusters of stars

● Clusters also contain stars Clusters also contain stars such as RR Lyrae or such as RR Lyrae or CephiedsCephieds– Variable starsVariable stars– `Pulse’ over days`Pulse’ over days– Pulsation period tells Pulsation period tells

you their brightnessyou their brightness– Bright enough to be Bright enough to be

seen in quite distant seen in quite distant clustersclusters

Distances to nearby galaxiesDistances to nearby galaxies

● Cepheids can even be seen Cepheids can even be seen in our galactic neighbors, in our galactic neighbors, so can measure distances so can measure distances to galaxies directly!to galaxies directly!

Electromagnetic RadiationElectromagnetic Radiation

● All these observations are All these observations are made with light, or some made with light, or some other form of other form of electromagnetic radiationelectromagnetic radiation

● Electromagnetic radiation Electromagnetic radiation from a source is in the form from a source is in the form of wavesof waves

● Both Electric and Magnetic Both Electric and Magnetic componentscomponents

● Wave travels at speed of Wave travels at speed of lightlight

Inverse Square LawInverse Square Law● Electromagnetic (and most other Electromagnetic (and most other

kinds) of radiation obey the kinds) of radiation obey the Inverse-Inverse-Square LawSquare Law

● Intensity of radiation (brightness) Intensity of radiation (brightness) falls off with the square of the falls off with the square of the distancedistance

– Doubling the distance to Doubling the distance to something makes it appear four something makes it appear four times as dim (¼ as bright)times as dim (¼ as bright)

– Tripling the distance makes it Tripling the distance makes it appear nine times as dim (1/9 as appear nine times as dim (1/9 as bright)bright)

– etc.etc.

Electromagnetic WavesElectromagnetic Waves

TV AntennaTV Antenna VHF: ~200 MHz; wavelength~60”VHF: ~200 MHz; wavelength~60” UHF: ~575 MHz; wavelength~20”UHF: ~575 MHz; wavelength~20”

15”

CB Radio AntennaCB Radio Antenna ~27 MHz; wavelength~ 36 ft~27 MHz; wavelength~ 36 ft

~9'

Satellite TV dishSatellite TV dish ~12 GHz; wavelength ~9”~12 GHz; wavelength ~9”

~4.5”

Electromagnetic WavesElectromagnetic Waves

● Light is one facet of the entire electromagnetic spectrumLight is one facet of the entire electromagnetic spectrum● Our eyes have dedicated cells which are sensitive to Our eyes have dedicated cells which are sensitive to

electromagnetic radiation in this rangeelectromagnetic radiation in this range● `Antenna' sensitive to light`Antenna' sensitive to light● Eyes most sensitive to yellow light – this is where the sun Eyes most sensitive to yellow light – this is where the sun

emits the peak amount of energyemits the peak amount of energy

What Generates Electromagnetic Waves?What Generates Electromagnetic Waves?

● Thermal radiationThermal radiation: Hot things glow.: Hot things glow.

– Heat causes atoms to rattle about in an objectHeat causes atoms to rattle about in an object– Atoms contain charged particles (electrons, Atoms contain charged particles (electrons,

protons)protons)– Accelerating charged particles emit Accelerating charged particles emit

electromagnetic radiation.electromagnetic radiation.● Other processesOther processes

– Nuclear reactionsNuclear reactions– Magnetic fields interacting with charged Magnetic fields interacting with charged

particlesparticles

Thermal RadiationThermal Radiation● If material is dense enough to be opaque, hot body emits If material is dense enough to be opaque, hot body emits

radiation in a characteristic `blackbody' spectrumradiation in a characteristic `blackbody' spectrum

● Hot objects emit Hot objects emit moremore and at and at shorter wavelengthsshorter wavelengths ((higher frequencies)higher frequencies)

High frequency Low frequencyShort wavelength Long wavelength

Line SpectraLine Spectra● For non-opaque materials, For non-opaque materials,

spectra can look quite spectra can look quite different.different.

● Atoms/molecules can emit Atoms/molecules can emit or absorb photons only of or absorb photons only of particular energies.particular energies.

● If dense enough, these lines If dense enough, these lines get blended out into get blended out into blackbody spectrumblackbody spectrum

● If not (like gas in flame) the If not (like gas in flame) the spectrum is composed of spectrum is composed of lineslines

Solar SpectrumSolar Spectrum

hot core

Wispier outer layersWispier outer layers

● Central region of sun fairly Central region of sun fairly dense dense

– Emits as blackbodyEmits as blackbody● Outer layers progressively less Outer layers progressively less

densedense

– Line effects start Line effects start becoming noticeablebecoming noticeable

● We see continuum blackbody We see continuum blackbody spectrum from the inner star spectrum from the inner star with absorption features from with absorption features from the outer layersthe outer layers

Solar SpectrumSolar SpectrumSolar SpectrumSolar Spectrum

CalciumCalcium

Hydrogen Hydrogen

SodiumSodiumOxygen MoleculesOxygen Molecules

The Sun throughout the spectrumThe Sun throughout the spectrum

The Galaxy throughout the spectrumThe Galaxy throughout the spectrum

Doppler Shift in LightDoppler Shift in Light

● Sound or light from a source moving towards Sound or light from a source moving towards you is shifted to higher frequencies (light is you is shifted to higher frequencies (light is bluer)bluer)

● From a source moving away from you, shifted to From a source moving away from you, shifted to lower frequencies (redder)lower frequencies (redder)

Doppler Shift in LightDoppler Shift in Light

● Effect is fairly modest, but spectra can be Effect is fairly modest, but spectra can be measured measured veryvery accurately accurately

● Astronomers can measure velocities Astronomers can measure velocities towards/away very preciselytowards/away very precisely

The Drake EquationThe Drake Equation

● Drake Equation structured the class until nowDrake Equation structured the class until now● AstronomyAstronomy

● Number of stars in galaxyNumber of stars in galaxy● Number of suitable starsNumber of suitable stars● Number of stars that form planetsNumber of stars that form planets

● GeophysicsGeophysics● Number of planets suitable for lifeNumber of planets suitable for life

● BiologyBiology● Where and low life forms on those planetsWhere and low life forms on those planets

Spiral GalaxiesSpiral Galaxies

● Flat, disk-shaped Flat, disk-shaped galaxies with spiral galaxies with spiral armsarms

● Rotate (our part of our Rotate (our part of our galaxy rotates around galaxy rotates around the center every ~200 the center every ~200 million years)million years)

● Gas clouds, dust, starsGas clouds, dust, stars

Elliptical GalaxiesElliptical Galaxies

● SpheroidalSpheroidal● FeaturelessFeatureless● Much brighter in core Much brighter in core

than in outer regionsthan in outer regions● Often the brightest Often the brightest

galaxies in clusters are galaxies in clusters are ellipticalsellipticals

● Less active in star Less active in star formtion / young stars formtion / young stars than spiralsthan spirals

Galaxies moving away from us!Galaxies moving away from us!

● Once `spiral nebulae’ Once `spiral nebulae’ were established as were established as galaxies, Hubble galaxies, Hubble examined their redshifts, examined their redshifts, and distancesand distances

● Found that galaxies were Found that galaxies were all moving away from us; all moving away from us; faster faster

Expanding UniverseExpanding Universe

● Either we are very special Either we are very special and everything is moving and everything is moving away from us, or Universe away from us, or Universe as a whole is expandingas a whole is expanding

● But if universe is steadily But if universe is steadily increasing in size, implies increasing in size, implies that at some time in the that at some time in the past, Universe was a past, Universe was a single point.single point.

● `Start of the Universe’`Start of the Universe’

– Big BangBig Bang

The Microwave backgroundThe Microwave background

● Accidentally discovered Accidentally discovered by radio astronomers by radio astronomers (thought it was noise)(thought it was noise)

● 1980s, COBE satellite 1980s, COBE satellite went up to take careful went up to take careful measurementsmeasurements

● Blackbody temperature Blackbody temperature agrees with predictionsagrees with predictions

● Slight fluctuations; hot Slight fluctuations; hot spots which eventually spots which eventually gave rise to galaxies!gave rise to galaxies!

`Big Bang’ Nucleosynthesis`Big Bang’ Nucleosynthesis

● Can also predict what nuclei are formed at such temperaturesCan also predict what nuclei are formed at such temperatures● Too cold: can’t form nucleiToo cold: can’t form nuclei● Too hot: large nuclei are torn apartToo hot: large nuclei are torn apart● Prediction: Universe should be mostly Hydrogen, Helium, some Prediction: Universe should be mostly Hydrogen, Helium, some

Lithium: Prediction agrees with observationLithium: Prediction agrees with observation

Stellar CycleStellar Cycle

Gas CloudsGas Clouds

● Two broad types of clouds:Two broad types of clouds:

– Gas cloudsGas clouds● WarmWarm● Very wispyVery wispy

– Molecular cloudsMolecular clouds● ColderColder● Much denserMuch denser● Gas has condensed Gas has condensed

enough that complex enough that complex molecules have formedmolecules have formed

Molecular CloudsMolecular Clouds

● Because molecular clouds are cooler and denser, atoms Because molecular clouds are cooler and denser, atoms collide more oftencollide more often

● Can form complex moleculesCan form complex molecules● Greatly helped by presence of grainsGreatly helped by presence of grains● Provides sites for atoms to latch ontoProvides sites for atoms to latch onto● Region of high atom density; atoms more easily find Region of high atom density; atoms more easily find

other atoms to interact withother atoms to interact with

Gas CloudsGas Clouds

● All of these gas clouds are turbulentAll of these gas clouds are turbulent● Random motions, eddiesRandom motions, eddies● Where fluid comes together, dense Where fluid comes together, dense

regionsregions● Fluid is moving fast enough that Fluid is moving fast enough that

can compress very dense spotscan compress very dense spots

Gas CloudsGas Clouds

● Gravity acts to try to pull Gravity acts to try to pull these dense spots togetherthese dense spots together

● However,However,

– Pressure in gas clouds Pressure in gas clouds – RotationRotation

Gas CloudsGas Clouds

● Collapse will usually Collapse will usually happen in many places happen in many places throughout the cloud at the throughout the cloud at the same time same time

● This is why stars tend to This is why stars tend to be clusteredbe clustered

● Amount of stars depends Amount of stars depends on size of gas cloud on size of gas cloud producing starsproducing stars

Protoplanetary Protoplanetary DisksDisks

● These protoplanetary These protoplanetary disks can be seen around disks can be seen around very young protostarsvery young protostars

Protoplanetary DisksProtoplanetary Disks

SummarySummary

Failed StarsFailed Stars

● `Stars' that are too small (~8% of `Stars' that are too small (~8% of the mass of the Sun, or ~80 Jupiter the mass of the Sun, or ~80 Jupiter masses) never ``turn on''masses) never ``turn on''

● Central temperatures never get hot Central temperatures never get hot enough for nuclear burning to enough for nuclear burning to begin in earnestbegin in earnest

● Nuclear burning is what powers Nuclear burning is what powers the star through its lifethe star through its life

● Star sits around as a brown dwarf – Star sits around as a brown dwarf – too big and hot to be a planet, too too big and hot to be a planet, too small and cold to be a real starsmall and cold to be a real star

Hydrostatic EquilibriumHydrostatic Equilibrium● Once collapse has halted in a star, Once collapse has halted in a star,

force inward (gravity) must be force inward (gravity) must be balanced by force outward (gas balanced by force outward (gas pressure)pressure)

● (Much of the rotation has been (Much of the rotation has been taken away by the planetary disk taken away by the planetary disk by this point)by this point)

● Central region is hottest because Central region is hottest because pressure from the entire star is pressure from the entire star is pushing down on itpushing down on it

● Star as a whole is hot enough that Star as a whole is hot enough that no molecules are left; everything is no molecules are left; everything is broken into componentsbroken into components

Nuclear ReactionsNuclear Reactions● Nuclei of atoms themselves Nuclei of atoms themselves

interactinteract● Change the elements: alchemyChange the elements: alchemy● The star, like the cloud it came The star, like the cloud it came

from, is mostly hydrogenfrom, is mostly hydrogen● So hot the electrons are stripped So hot the electrons are stripped

off; left with bare protons off; left with bare protons (hydrogen nuclei)(hydrogen nuclei)

● Under extreme heat, protons can Under extreme heat, protons can fuse together to produce helium: fuse together to produce helium: and more heat!and more heat!

● Higher temperatures – faster Higher temperatures – faster reactionsreactions

Given that burning is stable,Given that burning is stable,

● What effects how hot a star is?What effects how hot a star is?

– MASSMASS● The bigger the star that forms from the The bigger the star that forms from the

collapsecollapse

– More pressure on the central regionMore pressure on the central region– More burningMore burning– Hotter Hotter – BrighterBrighter

● What color are more massive stars?What color are more massive stars?

HR diagram and Main SequenceHR diagram and Main Sequence

● From previous, expect that From previous, expect that hotter stars should be brighterhotter stars should be brighter

– BlackbodyBlackbody– More massive -> biggerMore massive -> bigger

● Even more than this; bigger -> Even more than this; bigger -> more temperature in core -> more temperature in core -> more burning more burning

● When temperature vs brightness When temperature vs brightness is plotted, see `Main Sequence'is plotted, see `Main Sequence'

● Other populated regions show Other populated regions show later stages in stellar evolutionlater stages in stellar evolution

Stellar EvolutionStellar Evolution

● As burning in core progresses, As burning in core progresses, Hydrogen in center becomes Hydrogen in center becomes depleted (Sun: ~10 billion depleted (Sun: ~10 billion years)years)

● Core of Helium `ash' left behindCore of Helium `ash' left behind● Shell of Hydrogen burning Shell of Hydrogen burning

slowly moves outwardsslowly moves outwards● As heat source moves further As heat source moves further

out, star `puffs out'out, star `puffs out'● Outer regions cool, reddenOuter regions cool, redden● Red Giant (Sun: 1 billion years)Red Giant (Sun: 1 billion years)

Stellar EvolutionStellar Evolution

● Eventually Helium core gets so Eventually Helium core gets so hot that even it can burn, to hot that even it can burn, to CarbonCarbon

● New energy source: star gets New energy source: star gets hotter and bluer, and shrinks hotter and bluer, and shrinks back to more normal sizeback to more normal size

● Burning happens faster with Burning happens faster with heavier elements; soon Helium heavier elements; soon Helium becomes exhausted, a Carbon becomes exhausted, a Carbon core forms; becomes giant core forms; becomes giant againagain

Low Mass stars: envelope ejectionLow Mass stars: envelope ejection

● Helium burning can be very Helium burning can be very unstableunstable

● Outer layers begin pulsing; Outer layers begin pulsing; blows most of the envelope off blows most of the envelope off of the starof the star

● (so called) `Planetary nebula' (so called) `Planetary nebula' formsforms

● Only the core is left behind, still Only the core is left behind, still glowing (because hot) but inertglowing (because hot) but inert

● White dwarfWhite dwarf

High Mass Stars: Continue BurningHigh Mass Stars: Continue Burning

● Slightly more massive stars (4 Slightly more massive stars (4 to 8 solar masses):to 8 solar masses):

– Everything happens fasterEverything happens faster– Carbon can burn, as well; Carbon can burn, as well;

one more stage of burningone more stage of burning– Then again leave (larger) Then again leave (larger)

white dwarf and planetary white dwarf and planetary nebula behindnebula behind

Type II SupernovaType II Supernova

● The result is a collapse to a different The result is a collapse to a different form of matter – a neutron star, or a form of matter – a neutron star, or a black hole -- and a release of energyblack hole -- and a release of energy

● Energy release can be equal to the Energy release can be equal to the entire energy of the host galaxyentire energy of the host galaxy

● Entire envelope is blown apart Entire envelope is blown apart

– Heavy elements from burning Heavy elements from burning blown into surrounding gasblown into surrounding gas

Type Ia SupernovaType Ia Supernova

● Almost as much energy can come Almost as much energy can come from another kind of supernovafrom another kind of supernova

● If a star which ended up as a white If a star which ended up as a white dwarf has a companion, matter can dwarf has a companion, matter can `rain in' on the inert white dwarf until `rain in' on the inert white dwarf until it gets hot enough to burnit gets hot enough to burn

● Can burn catastrophically, exploding Can burn catastrophically, exploding and releasing heat, heavy elements and releasing heat, heavy elements into surrounding gasinto surrounding gas

Supernova FeedbackSupernova Feedback● Originally, gas was all hydrogen and heliumOriginally, gas was all hydrogen and helium

– No planets, lifeNo planets, life● Generations of stars produced all the heavy elements Generations of stars produced all the heavy elements

which make up planets and living thingswhich make up planets and living things● Supernova explosions release these heavy elements into Supernova explosions release these heavy elements into

the galaxythe galaxy

– New stars are formedNew stars are formed– Can make planets, lifeCan make planets, life

● Supernova energy contributes to the turbulence in the Supernova energy contributes to the turbulence in the gas clouds, and can compress gas to start new cycle of gas clouds, and can compress gas to start new cycle of star formationstar formation

Supermassive starsSupermassive stars

● Newly discovered:Newly discovered:

– LBV 1806-20LBV 1806-20● 150x as massive as Sun150x as massive as Sun● 4- to 20-million times as bright 4- to 20-million times as bright

as sunas sun

Supermassive starsSupermassive stars

● Question:Question:

– If 150x as massive, If 150x as massive, 10million times as bright 10million times as bright as Sun, how long will it as Sun, how long will it last?last?

Supermassive starsSupermassive stars

● Question:Question:

– If 150x as massive, If 150x as massive, 10million times as bright 10million times as bright as Sun, how far away as Sun, how far away does planet need to be to does planet need to be to have Earth-like have Earth-like conditions?conditions?

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.

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

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

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

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

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

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!

Marks – Reading Quizzes and AssignmentsMarks – Reading Quizzes and Assignments

● Reading Quiz:Reading Quiz:

– 0 NCR, 4 NCR+, 7 CR, 8 CR+, 0 CR++0 NCR, 4 NCR+, 7 CR, 8 CR+, 0 CR++● Assignments:Assignments:

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

Exponential GrowthExponential Growth● Such growth is said to be Such growth is said to be

exponential, or geometric.exponential, or geometric.● Once the process is Once the process is

exponential, everything is exponential, everything is exponential:exponential:

– Number of childrenNumber of children– Number of reproductionsNumber of reproductions– Amount of area/resources Amount of area/resources

neededneeded– Rate of growthRate of growth

● Anything with a fixed Anything with a fixed `doubling time' is exponential`doubling time' is exponential

Exponential GrowthExponential Growth● This exponential growth is the This exponential growth is the

source of the intense source of the intense competition for resources competition for resources underlying evolutionary underlying evolutionary adaptationadaptation

● Very soon, resources begin Very soon, resources begin getting scarce; any species or getting scarce; any species or mutation which has an mutation which has an advantge has a much better advantge has a much better chance of thrivingchance of thriving

Exponential GrowthExponential Growth● Everything starts happening Everything starts happening

faster as exponential growth faster as exponential growth proceedsproceeds

● Mutation rate; in mammals, ~1 Mutation rate; in mammals, ~1 per 100,000 reproductions per per 100,000 reproductions per genegene

● By generation 10, ~512 By generation 10, ~512 individuals. How long before individuals. How long before significant number of significant number of mutations expected in a given mutations expected in a given gene?gene?

Exponential GrowthExponential Growth● Everything is exponentialEverything is exponential● By generation 20, already By generation 20, already

expect ~20 mutationsexpect ~20 mutations● That too is exponentially That too is exponentially

increasingincreasing● By generation 25, > 600By generation 25, > 600● By generation 30, > 20000By generation 30, > 20000● Dividing by 100,000 just Dividing by 100,000 just

means it takes a little longer means it takes a little longer before it takes offbefore it takes off

Tree of LifeTree of Life● Phylogenetic treePhylogenetic tree● `Family Tree' of species`Family Tree' of species● Distance from neighbors, root Distance from neighbors, root

indicates how genetically differentindicates how genetically different● Three distinct branches:Three distinct branches:

– Archaea (includes Archaea (includes `extremophiles)`extremophiles)

– BacteriaBacteria– Eukaryotes (includes all life Eukaryotes (includes all life

visible to naked eye)visible to naked eye)

Building a Phylogenetic TreeBuilding a Phylogenetic Tree● Difficult: Only have genetic Difficult: Only have genetic

information from the present.information from the present.● Can take genetic informtion from Can take genetic informtion from

present day species and examine present day species and examine differencesdifferences

● Number of differences in genome: Number of differences in genome: `genetic distance'`genetic distance'

● Simplest: if constant mutation rate, Simplest: if constant mutation rate, can work backwards and see how can work backwards and see how long ago two species must have long ago two species must have first differedfirst differed

● Can infer most recent common Can infer most recent common ancestorancestor

Genetic Distance

Evo

luti

on T

ime

Inferred ancestor

Inferred ancestor

VirusVirus

● Not IncludedNot Included● Self-replicating DNA or RNASelf-replicating DNA or RNA● Not self sufficientNot self sufficient● Requires the mechanisms of a living cell Requires the mechanisms of a living cell

to propagate itto propagate it● As a result, much smaller than bacteria As a result, much smaller than bacteria

(largest virus ~ smallest bacteria)(largest virus ~ smallest bacteria)

VirusVirus

● Alive?Alive?

– Inert RNA/DNA/protein until Inert RNA/DNA/protein until collides with target cellcollides with target cell

– Incapable of independent action, Incapable of independent action, growth, reproductiongrowth, reproduction

– Not generally considered to be Not generally considered to be living.living.

ProkaryotesProkaryotes

● Simplest form of lifeSimplest form of life● Includes bacteria (like E. Coli) Includes bacteria (like E. Coli)

and archaebacteriaand archaebacteria● No complex internal structureNo complex internal structure● DNA lies together in a blobDNA lies together in a blob● Prokaryotic DNA consists of one Prokaryotic DNA consists of one

ringring● Processes occur throughout cellProcesses occur throughout cell● Many reproduce by cell division Many reproduce by cell division

(asexual)(asexual)

ExtremophilesExtremophiles

● Unlike more Unlike more `advanced' `advanced' forms of life, prokaryotes thrive forms of life, prokaryotes thrive in startling variety of in startling variety of environmentsenvironments

● Can live with, without, or only Can live with, without, or only without oxygenwithout oxygen

● Can live in very acidic, alkaline, Can live in very acidic, alkaline, hot, cold, dark, or salty hot, cold, dark, or salty enviromentsenviroments

● Early earth would have been Early earth would have been rich with these enviromentsrich with these enviroments

M. Jannaschii thrives near underwater volcanic vents in

temperatures, pressures, darkness, and lack of oxygen that would kill

other life

PhotosynthesisPhotosynthesis

● A process that uses light A process that uses light energy to convert water, energy to convert water, carbon dioxide to sugar (a carbon dioxide to sugar (a useful fuel) plus oxygenuseful fuel) plus oxygen

● Clorophyll is the key Clorophyll is the key molecule in this processmolecule in this process

● Absorbs some light, triggers Absorbs some light, triggers a chemical reactiona chemical reaction

6 H2O + 6 CO

2 -> C

6H

12O

6 + 6 O

2

EukaryotesEukaryotes

● Has a nucleus, and other Has a nucleus, and other `organelles’`organelles’

● DIVISION OF LABOURDIVISION OF LABOUR● Mitocondrion: energy Mitocondrion: energy

factoryfactory● Chloroplast (plants): Chloroplast (plants):

photosynthesisphotosynthesis● Nucleus: protects DNA; Nucleus: protects DNA;

interface between DNA and interface between DNA and rest of cellrest of cell

Sexual ReproductionSexual Reproduction

● Allows greater mixing of Allows greater mixing of genesgenes

● Rather than waiting for Rather than waiting for single mutation, can have single mutation, can have combination of genes combination of genes randomly generatedrandomly generated

● Greatly speeds up Greatly speeds up evolutionary process for evolutionary process for complex organisms where complex organisms where genes interact.genes interact.

Cambrian ExplosionCambrian Explosion

● Soon after the arrival of Soon after the arrival of eukaryotes on the scene, eukaryotes on the scene, there was a huge explosion there was a huge explosion of speciesof species

● Cambrian ExplosionCambrian Explosion● Exponential growth -> one Exponential growth -> one

expects this, but before expects this, but before sexual reproduction, sexual reproduction, evolution occurred much evolution occurred much more slowlymore slowly

Multicellular lifeMulticellular life

● So many possibilities that So many possibilities that they never appear to repeatthey never appear to repeat

● Trilobite, an enormously Trilobite, an enormously successful multicellular successful multicellular animal, thrived for tens of animal, thrived for tens of millions of years; extinct millions of years; extinct with dinasaurswith dinasaurs

● Never to reappearNever to reappear● On the other hand, a On the other hand, a

successful species can successful species can survive indefinately (?)survive indefinately (?)– Blue-Green Algae Blue-Green Algae

Next WeekNext Week

● Reading: Chapter 11, 12Reading: Chapter 11, 12

– Brief History of Solar SystemBrief History of Solar System– Examination of VenusExamination of Venus

● Guest lecturer: Andrew Puckett, University of ChicagoGuest lecturer: Andrew Puckett, University of Chicago