End-of-Term Projects

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End-of-Term Projects

• In class, May 14th for both presentations and
  reports
• Reports
• 12 pp on material which is relevant to course
• Presentations
• 20min, hand in a 1p summary
• Worth 10 pts (5 assignments)
• Grades due May 17th NOTHING ACCEPTED after class
  time on 14th.
• Can pick up marked copies from my mailbox

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Search for Life In the Universe Best Of'
Edition.

• Clip Show 1 The Science behind the Search

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Science in a Nutshell
Observations (reality)
Consequences(predictions)
Explanation(theory)
Tests
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Science in a Nutshell

• The universe is understandable
• Scientific knowledge is forever
• Scientific ideas are subject to change
• Science demands evidence
• Science explains and predicts

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Careful Observation

• Careful observation is the beginnings of all
  science.
• Observations can be of the world as it is or of
  carefully set up situations to see what happens
  (experiments)
• In some sciences experimentation isn't possible
  (astronomy) or is limited (human behavior), and
  only observations are feasible
• Making careful observations isn't as easy as it
  may seem.

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Overthrow-ability of Theories

• Theories can be disproven by finding evidence
  which contrdicts them.
• (Evidence itself must be verified data might be
  wrong)
• Any new theory must explain everything that
  previous theory did, plus the new evidence.

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Complexity in Life

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

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Chemistry of Life

• Chemistry has as building blocks the elements
  around us.
• Big bang produced mainly Hydrogen, Helium
• Sun Everything's Hydrogen, Helium, Oxygen,
  Carbon, small traces of other stuff Pop I star
• Earth Richer in heavier stuff (Iron,
  Silicon,...)
• Other stars, planets likely to be similar
• Relative abundances of (Hydrogen, Helium) and
  (Carbon, Oxygen, Silicon, Iron...) may vary
• Of these building blocks, what chemicals can
  build complex chemistry?

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Chemistry of life Carbon

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

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Chemistry of life Water?

• Water is essential to life on earth
• Thought that life began in the water (more on
  that in later lectures)
• For chemical life, need a way to get chemicals to
  different part of the body
• Water is a very powerful solvent.
• Dissolve chemical
• Allow transport through body in liquid form
• Very few liquid solvents as powerful, or as
  common.

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Limitations of water

• If life depends on water, then very strict limit
  on where life can be
• Can't be anywhere colder than freezing
• Can't be anywhere hotter than boiling
• Other liquid solvents have different
  freezing/boiling points, but problem remains
• Hard to see how chemicals can be efficiently
  transported through a body otherwise

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Water On Mars

• Current Mars rover saw spherules'
  (blueberries') in many places
• Could indicate water
• Form as concretions'
• Speck of something in water
• Other sediments build up
• Same process as pearls, snowflakes, raindrops
• But other possibilities

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Water On Mars

• Other evidence rock formations
• Suggestive of water erosion
• In particular, spherule formed inside crack in
  rock
• Evidence that spherule did form through
  concretion
• Cracks seem to be from water rivulets

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Water On Mars

• More evidence build up of sulfates, other salts
  on surface
• Very strong evidence that water laced with
  minerals was flowing
• When evaporated, left these minerals behind

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Water On Mars

• No evidence yet of life
• Water would seem to be a necessary ingredient
• No evidence for oceans, or that Mars was warm
  enough to have liquid water for long time

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What sort of life are we interested in?

• In our own solar system, even bacteria fossils
  would be enormous find.
• Have some chance of looking at Mars, other nearby
  planets
• For life outside our solar system, won't be able
  to visit for foreseeable future
• Only way to recognize life is to receive signals
• Life must be intelligent enough to communicate
  with us in a way we can recognize

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The Distance Ladder

• Four realms' of distance in exploring Universe
• Solar system
• Nearby stars
• Galactic distances
• Intergalactic distance
• So vastly different that each needs different
  techniques, units to measure distances

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Solar System

• Can use direct observation, simple geometry to
  measure solar system distances to reasonable
  accuracy
• These were available to the ancients
• More modern techniques (radar, spacecraft..)
  allow increased accuracy

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New length unit Astronomical Unit (AU)

• Earth-Sun distance so handy for measuring solar
  system distances that new unit created
• 1 AU mean distance between Earth and Sun
• 1 AU 92,955,807 miles
• Can use this information to work way up to next
  realm nearby stars

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Paralaxes can be observed in stars
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Paralaxes can be observed in stars
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The displacement is measured as an angle on the
sky

• 0.5 degree about your thumb at arms length
• 1 arc minute 1/60th of a degree
• 1 arc second 1/60th of an arc minute
• A distance at which the parallax (from Jan to
  Mar) is 1 arc second is a parsec (PARallax
  SECond)
• Can find it from 1 AU with some trig
• 1 pc 206265 AU

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Distances to distant clusters of stars

• Clusters also contain stars such as RR Lyrae or
  Cephieds
• Variable stars
• Pulse over days
• Pulsation period tells you their brightness
• Bright enough to be seen in quite distant clusters

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Distances to nearby galaxies

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

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Electromagnetic Radiation

• All these observations are made with light, or
  some other form of electromagnetic radiation
• Electromagnetic radiation from a source is in the
  form of waves
• Both Electric and Magnetic components
• Wave travels at speed of light

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Inverse Square Law

• Electromagnetic (and most other kinds) of
  radiation obey the Inverse-Square Law
• Intensity of radiation (brightness) falls off
  with the square of the distance
• Doubling the distance to something makes it
  appear four times as dim (¼ as bright)
• Tripling the distance makes it appear nine times
  as dim (1/9 as bright)
• etc.

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Electromagnetic Waves
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9'
TV Antenna VHF 200 MHz wavelength60 UHF
575 MHz wavelength20
4.5
CB Radio Antenna 27 MHz wavelength 36 ft
Satellite TV dish 12 GHz wavelength 9
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Electromagnetic Waves

• Light is one facet of the entire electromagnetic
  spectrum
• Our eyes have dedicated cells which are sensitive
  to electromagnetic radiation in this range
• Antenna' sensitive to light
• Eyes most sensitive to yellow light this is
  where the sun emits the peak amount of energy

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What Generates Electromagnetic Waves?

• Thermal radiation Hot things glow.
• Heat causes atoms to rattle about in an object
• Atoms contain charged particles (electrons,
  protons)
• Accelerating charged particles emit
  electromagnetic radiation.
• Other processes
• Nuclear reactions
• Magnetic fields interacting with charged particles

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Thermal Radiation

• If material is dense enough to be opaque, hot
  body emits radiation in a characteristic
  blackbody' spectrum

High frequency
Low frequency
Short wavelength
Long wavelength

• Hot objects emit more and at shorter wavelengths
  (higher frequencies)

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Line Spectra

• For non-opaque materials, spectra can look quite
  different.
• Atoms/molecules can emit or absorb photons only
  of particular energies.
• If dense enough, these lines get blended out into
  blackbody spectrum
• If not (like gas in flame) the spectrum is
  composed of lines

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Solar Spectrum

• Central region of sun fairly dense
• Emits as blackbody
• Outer layers progressively less dense
• Line effects start becoming noticeable
• We see continuum blackbody spectrum from the
  inner star with absorption features from the
  outer layers

hot core
Wispier outer layers
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Solar Spectrum
Solar Spectrum
Calcium
Oxygen Molecules
Sodium
Hydrogen
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The Sun throughout the spectrum
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The Galaxy throughout the spectrum
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Doppler Shift in Light

• Sound or light from a source moving towards you
  is shifted to higher frequencies (light is bluer)
• From a source moving away from you, shifted to
  lower frequencies (redder)

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Doppler Shift in Light

• Effect is fairly modest, but spectra can be
  measured very accurately
• Astronomers can measure velocities towards/away
  very precisely

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The Drake Equation

• Drake Equation structured the class until now
• Astronomy
• Number of stars in galaxy
• Number of suitable stars
• Number of stars that form planets
• Geophysics
• Number of planets suitable for life
• Biology
• Where and low life forms on those planets

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Spiral Galaxies

• Flat, disk-shaped galaxies with spiral arms
• Rotate (our part of our galaxy rotates around the
  center every 200 million years)
• Gas clouds, dust, stars

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Elliptical Galaxies

• Spheroidal
• Featureless
• Much brighter in core than in outer regions
• Often the brightest galaxies in clusters are
  ellipticals
• Less active in star formtion / young stars than
  spirals

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Galaxies moving away from us!

• Once spiral nebulae were established as
  galaxies, Hubble examined their redshifts, and
  distances
• Found that galaxies were all moving away from us
  faster

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Expanding Universe

• Either we are very special and everything is
  moving away from us, or Universe as a whole is
  expanding
• But if universe is steadily increasing in size,
  implies that at some time in the past, Universe
  was a single point.
• Start of the Universe
• Big Bang

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The Microwave background

• Accidentally discovered by radio astronomers
  (thought it was noise)
• 1980s, COBE satellite went up to take careful
  measurements
• Blackbody temperature agrees with predictions
• Slight fluctuations hot spots which eventually
  gave rise to galaxies!

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Big Bang Nucleosynthesis

• Can also predict what nuclei are formed at such
  temperatures
• Too cold cant form nuclei
• Too hot large nuclei are torn apart
• Prediction Universe should be mostly Hydrogen,
  Helium, some Lithium Prediction agrees with
  observation

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Stellar Cycle
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Gas Clouds

• Two broad types of clouds
• Gas clouds
• Warm
• Very wispy
• Molecular clouds
• Colder
• Much denser
• Gas has condensed enough that complex molecules
  have formed

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Molecular Clouds

• Because molecular clouds are cooler and denser,
  atoms collide more often
• Can form complex molecules
• Greatly helped by presence of grains
• Provides sites for atoms to latch onto
• Region of high atom density atoms more easily
  find other atoms to interact with

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Gas Clouds

• All of these gas clouds are turbulent
• Random motions, eddies
• Where fluid comes together, dense regions
• Fluid is moving fast enough that can compress
  very dense spots

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Gas Clouds

• Gravity acts to try to pull these dense spots
  together
• However,
• Pressure in gas clouds
• Rotation

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Gas Clouds

• Collapse will usually happen in many places
  throughout the cloud at the same time
• This is why stars tend to be clustered
• Amount of stars depends on size of gas cloud
  producing stars

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Protoplanetary Disks

• These protoplanetary disks can be seen around
  very young protostars

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Protoplanetary Disks
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Summary
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Failed Stars

• Stars' that are too small (8 of the mass of
  the Sun, or 80 Jupiter masses) never turn on''
• Central temperatures never get hot enough for
  nuclear burning to begin in earnest
• Nuclear burning is what powers the star through
  its life
• Star sits around as a brown dwarf too big and
  hot to be a planet, too small and cold to be a
  real star

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Hydrostatic Equilibrium

• Once collapse has halted in a star, force inward
  (gravity) must be balanced by force outward (gas
  pressure)
• (Much of the rotation has been taken away by the
  planetary disk by this point)
• Central region is hottest because pressure from
  the entire star is pushing down on it
• Star as a whole is hot enough that no molecules
  are left everything is broken into components

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Nuclear Reactions

• Nuclei of atoms themselves interact
• Change the elements alchemy
• The star, like the cloud it came from, is mostly
  hydrogen
• So hot the electrons are stripped off left with
  bare protons (hydrogen nuclei)
• Under extreme heat, protons can fuse together to
  produce helium and more heat!
• Higher temperatures faster reactions

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Given that burning is stable,

• What effects how hot a star is?
• MASS
• The bigger the star that forms from the collapse
• More pressure on the central region
• More burning
• Hotter
• Brighter
• What color are more massive stars?

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HR diagram and Main Sequence

• From previous, expect that hotter stars should be
  brighter
• Blackbody
• More massive -gt bigger
• Even more than this bigger -gt more temperature
  in core -gt more burning
• When temperature vs brightness is plotted, see
  Main Sequence'
• Other populated regions show later stages in
  stellar evolution

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Stellar Evolution

• As burning in core progresses, Hydrogen in center
  becomes depleted (Sun 10 billion years)
• Core of Helium ash' left behind
• Shell of Hydrogen burning slowly moves outwards
• As heat source moves further out, star puffs
  out'
• Outer regions cool, redden
• Red Giant (Sun 1 billion years)

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Stellar Evolution

• Eventually Helium core gets so hot that even it
  can burn, to Carbon
• New energy source star gets hotter and bluer,
  and shrinks back to more normal size
• Burning happens faster with heavier elements
  soon Helium becomes exhausted, a Carbon core
  forms becomes giant again

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Low Mass stars envelope ejection

• Helium burning can be very unstable
• Outer layers begin pulsing blows most of the
  envelope off of the star
• (so called) Planetary nebula' forms
• Only the core is left behind, still glowing
  (because hot) but inert
• White dwarf

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High Mass Stars Continue Burning

• Slightly more massive stars (4 to 8 solar
  masses)
• Everything happens faster
• Carbon can burn, as well one more stage of
  burning
• Then again leave (larger) white dwarf and
  planetary nebula behind

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Type II Supernova

• The result is a collapse to a different form of
  matter a neutron star, or a black hole -- and a
  release of energy
• Energy release can be equal to the entire energy
  of the host galaxy
• Entire envelope is blown apart
• Heavy elements from burning blown into
  surrounding gas

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Type Ia Supernova

• Almost as much energy can come from another kind
  of supernova
• If a star which ended up as a white dwarf has a
  companion, matter can rain in' on the inert
  white dwarf until it gets hot enough to burn
• Can burn catastrophically, exploding and
  releasing heat, heavy elements into surrounding
  gas

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Supernova Feedback

• Originally, gas was all hydrogen and helium
• No planets, life
• Generations of stars produced all the heavy
  elements which make up planets and living things
• Supernova explosions release these heavy elements
  into the galaxy
• New stars are formed
• Can make planets, life
• Supernova energy contributes to the turbulence in
  the gas clouds, and can compress gas to start new
  cycle of star formation

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Supermassive stars

• Newly discovered
• LBV 1806-20
• 150x as massive as Sun
• 4- to 20-million times as bright as sun

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Supermassive stars

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

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Supermassive stars

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

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Abundance of Elements

• Hydrogen and Helium most abundant in Universe
  (from Big Bang)
• Not most abundant on rocky planets evaporation
• Heavy elements produced in stars, and will follow
  similar overall pattern
• Systems that have material processed by more
  stars will have overall more heavy elements
  compared to H, He.

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Building Blocks of Life

• These machinery of life is made of polymers
• Built out of chains of simpler molecules
  (monomers)
• modular'
• Three important polymers in Earth's biology
• Proteins
• Building blocks for everything
• DNA
• Repository of genetic information
• RNA
• Takes information from DNA, builds proteins

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Things are Very Different when you're a Molecule

• Gravity is not so important
• Electrical, molecular forces are
• WATER
• Constantly jostled by water molecules
• Some parts of molecules attracted to water
  (hydrophilic)
• Some parts repelled (hydrophobic)
• Molecules behave like little machines that are
  pushed around by electrical forces

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Proteins

• Proteins are long strings of amino acids
• The strings fold into complex shapes as they form
• Buffeted by water
• Bonds linking one part of chain to the other

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Proteins

• A protein's function is determined by it's shape
  or structure.
• It's structure is determined by the amino acids
  its made up of
• Enzymes are proteins which speed up certain
  reactions
• Maltase breaks maltose down into two glucose
  molecules
• Maltose fits into active site'
• Lock-and-key
• E. Coli has 1000 different proteins

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Amino Acids

• Building blocks of proteins
• Twenty of them occur in Earth's biology
• Simple molecules 13 27 atoms
• Carbon, Hydrogen, Oxygen, Nitrogen two also have
  Sulfur
• Chemically identical mirror images of these
  compounds (right-handed versions) do not occur in
  Earth's biology
• Typical protein might be built of 100 amino
  acids

tyrosine
alanine
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Nucleic Acids

• Proteins are encoded in a cell's DNA, and built
  on a scaffold' of RNA.
• RNA and DNA are both polymers of nucleotides
  molecules with bases as shown here
• Both DNA and RNA have an alphabet' of 4 bases

(DNA only)
(RNA only)
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Nucleotides

• These bases attach to a sugar and phosphate to
  form nucleotides
• These nucleotides are the monomers that make up
  DNA, RNA
• Sugar, phosphate makes up the backbone of the
  structure, with the base sticking out

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DNA

• A strand of DNA contains a long series of
  nucleotides, in a series of genes (AAGCTC...)
• Each gene is separated by a stop signal
• Contains all the information for making all the
  proteins in the cell

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DNA

• Proteins are made when an enzyme walks long the
  DNA strand, transcribing it into an RNA strand
• The RNA strand then gets translated into a
  protein.
• Each 3 letter' sequence gets translated into a
  single amino acid
• 64 possible 3-letter sequences 20 amino acids
• Some acids have several translations

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Reproduction

• This interwoven complementary pair' makes
  replication fairly straightforward
• Enzymes can march along the strand, separating it
  in two
• Each strand can then be matched up with the
  corresponding nucleotides, and rebuild its second
  half
• One twisted pair becomes two, containing same
  information

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Earth's Formation

• Condensed out of solar disk
• Small pieces (planetesimals) merging together
• Very hot radioactive materials, collisions
• Ultraviolet radiation from sun (no protecting
  ozone)
• Photodissociation
• Crust takes a long time to form
• Very geothermally active

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Atmosphere

• Probably never had an atmosphere that formed with
  the planet planetsimals too small to capture
  atmosphere
• As Earth becomes massive enough to trap gases,
  atmosphere forms as colliding objects
  (late-accreting material) are vaporized
• Volatile elements (lightest and easiest to
  vaporize) can most easily diffuse away
• Hydrogen, carbon, nitrogen, oxygen
• Free hydrogen most easily evaporated
• Photodissociation breaks up molecules

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Evolution of Atmosphere

• As hydrogen leaves, ozone can form
• Less hydrogen to suck up free oxygen into water
• Cuts down ultraviolet light, photodissociation
• Atmosphere begins to stabilize
• Water vapor
• Carbon Dioxide
• Nitrogen
• Carbon Monoxide
• Very little Oxygen
• Even less Ozone

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Miller-Urey Experiment

• 1953 here in Chicago
• Simulates oceans and atmosphere of a young Earth
• Ammonia, methane, hydrogen in atmosphere
• After only a few days, two amino acids and the
  nucleotide bases have formed!

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Marks Reading Quizzes and Assignments

• Reading Quiz
• 0 NCR, 4 NCR, 7 CR, 8 CR, 0 CR
• Assignments
• 0 NCR, 0 NCR, 4 CR, 9 CR, 1 CR

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Exponential Growth

• Such growth is said to be exponential, or
  geometric.
• Once the process is exponential, everything is
  exponential
• Number of children
• Number of reproductions
• Amount of area/resources needed
• Rate of growth
• Anything with a fixed doubling time' is
  exponential

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Exponential Growth

• This exponential growth is the source of the
  intense competition for resources underlying
  evolutionary adaptation
• Very soon, resources begin getting scarce any
  species or mutation which has an advantge has a
  much better chance of thriving

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Exponential Growth

• Everything starts happening faster as exponential
  growth proceeds
• Mutation rate in mammals, 1 per 100,000
  reproductions per gene
• By generation 10, 512 individuals. How long
  before significant number of mutations expected
  in a given gene?

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Exponential Growth

• Everything is exponential
• By generation 20, already expect 20 mutations
• That too is exponentially increasing
• By generation 25, gt 600
• By generation 30, gt 20000
• Dividing by 100,000 just means it takes a little
  longer before it takes off

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Tree of Life

• Phylogenetic tree
• Family Tree' of species
• Distance from neighbors, root indicates how
  genetically different
• Three distinct branches
• Archaea (includes extremophiles)
• Bacteria
• Eukaryotes (includes all life visible to naked
  eye)

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Building a Phylogenetic Tree

• Difficult Only have genetic information from the
  present.
• Can take genetic informtion from present day
  species and examine differences
• Number of differences in genome genetic
  distance'
• Simplest if constant mutation rate, can work
  backwards and see how long ago two species must
  have first differed
• Can infer most recent common ancestor

Inferred ancestor
Inferred ancestor
Evolution Time
Genetic Distance
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Virus

• Not Included
• Self-replicating DNA or RNA
• Not self sufficient
• Requires the mechanisms of a living cell to
  propagate it
• As a result, much smaller than bacteria (largest
  virus smallest bacteria)

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Virus

• Alive?
• Inert RNA/DNA/protein until collides with target
  cell
• Incapable of independent action, growth,
  reproduction
• Not generally considered to be living.

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Prokaryotes

• Simplest form of life
• Includes bacteria (like E. Coli) and
  archaebacteria
• No complex internal structure
• DNA lies together in a blob
• Prokaryotic DNA consists of one ring
• Processes occur throughout cell
• Many reproduce by cell division (asexual)

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Extremophiles

• Unlike more advanced' forms of life,
  prokaryotes thrive in startling variety of
  environments
• Can live with, without, or only without oxygen
• Can live in very acidic, alkaline, hot, cold,
  dark, or salty enviroments
• Early earth would have been rich with these
  enviroments

M. Jannaschii thrives near underwater volcanic
vents in temperatures, pressures, darkness, and
lack of oxygen that would kill other life
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Photosynthesis

• A process that uses light energy to convert
  water, carbon dioxide to sugar (a useful fuel)
  plus oxygen
• Clorophyll is the key molecule in this process
• Absorbs some light, triggers a chemical reaction

6 H2O 6 CO2 -gt C6H12O6 6 O2
98
Eukaryotes

• Has a nucleus, and other organelles
• DIVISION OF LABOUR
• Mitocondrion energy factory
• Chloroplast (plants) photosynthesis
• Nucleus protects DNA interface between DNA and
  rest of cell

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Sexual Reproduction

• Allows greater mixing of genes
• Rather than waiting for single mutation, can have
  combination of genes randomly generated
• Greatly speeds up evolutionary process for
  complex organisms where genes interact.

100
Cambrian Explosion

• Soon after the arrival of eukaryotes on the
  scene, there was a huge explosion of species
• Cambrian Explosion
• Exponential growth -gt one expects this, but
  before sexual reproduction, evolution occurred
  much more slowly

101
Multicellular life

• So many possibilities that they never appear to
  repeat
• Trilobite, an enormously successful multicellular
  animal, thrived for tens of millions of years
  extinct with dinasaurs
• Never to reappear
• On the other hand, a successful species can
  survive indefinately (?)
• Blue-Green Algae

102
Next Week

• Reading Chapter 11, 12
• Brief History of Solar System
• Examination of Venus
• Guest lecturer Andrew Puckett, University of
  Chicago