Transcript Lecture (Powerpoint)

End-of-Term Projects
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In class, May 14th for both presentations and
reports
Reports:
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Presentations:
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~12 pp on material which is relevant to
course
~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
Search for Life In the Universe: `Best Of'
Edition.
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Clip Show #1: The Science behind the Search
Science in a Nutshell
Observations (reality)
Explanation
(theory)
Tests
Consequences
(predictions)
Science in a Nutshell
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The universe is understandable
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Scientific knowledge is forever
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Scientific ideas are subject to change
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Science demands evidence
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Science explains and predicts
Careful Observation
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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.
Overthrow-ability of Theories
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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.
Complexity in Life
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Even the simplest life form has a lot more going
on than even fairly complex non-alive things
Chemistry of Life
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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
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Earth: Richer in heavier stuff (Iron, Silicon,...)
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Other stars, planets likely to be similar
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Relative abundances of (Hydrogen, Helium) and
(Carbon, Oxygen, Silicon, Iron...) may vary
Of these building blocks, what chemicals can
build complex chemistry?
Chemistry of life: Carbon
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Of plentiful stuff, Carbon (alone) can build very
complex molecules
Chemistry of life: Water?
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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.
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Dissolve chemical
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Allow transport through body in liquid
form
Very few liquid solvents as powerful, or as
common.
Limitations of water
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If life depends on water, then very strict limit on
where life can be
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Can't be anywhere colder than freezing
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Can't be anywhere hotter than boiling
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Other liquid solvents have different
freezing/boiling points, but problem remains
Hard to see how chemicals can be efficiently
transported through a body otherwise
Water On Mars
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Current Mars rover saw
`spherules' (`blueberries') in
many places
Could indicate water
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Form as `concretions'
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Speck of something in
water
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Other sediments build up
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Same process as pearls,
snowflakes, raindrops
But other possibilities
Water On Mars
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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
Water On Mars
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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
Water On Mars
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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
What sort of life are we interested in?
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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
The Distance Ladder
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Four `realms' of
distance in exploring
Universe
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Solar system
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Nearby stars
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Galactic distances
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Intergalactic
distance
So vastly different that
each needs different
techniques, units to
measure distances
Solar System
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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
New length unit: Astronomical Unit
(AU):
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Earth-Sun distance so handy for measuring solar
system distances that new unit created:
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1 AU = mean distance between Earth and Sun
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1 AU = 92,955,807 miles
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Can use this information to work way up to next
realm: nearby stars
Paralaxes can be observed in stars
Paralaxes can be observed in stars
The displacement is measured as an
angle on the sky
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0.5 degree: about your thumb at arms length
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1 arc minute: 1/60th of a degree
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1 arc second: 1/60th of an arc minute
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A distance at which the parallax (from Jan to
Mar) is 1 arc second is a parsec (PARallax
SECond)
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Can find it from 1 AU with some trig
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1 pc = 206265 AU
Distances to distant clusters of stars
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Clusters also contain stars
such as RR Lyrae or
Cephieds
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Variable stars
`Pulse’ over days
Pulsation period tells
you their brightness
Bright enough to be
seen in quite distant
clusters
Distances to nearby galaxies
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Cepheids can even be seen
in our galactic neighbors,
so can measure distances
to galaxies directly!
Electromagnetic Radiation
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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
Inverse Square Law
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Electromagnetic (and most other
kinds) of radiation obey the InverseSquare Law
Intensity of radiation (brightness)
falls off with the square of the
distance
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Doubling the distance to
something makes it appear
four times as dim (¼ as bright)
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Tripling the distance makes it
appear nine times as dim (1/9
as bright)
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etc.
Electromagnetic Waves
15”
~9'
TV Antenna
VHF: ~200 MHz; wavelength~60”
UHF: ~575 MHz; wavelength~20”
~4.5”
Satellite TV dish
~12 GHz; wavelength ~9”
CB Radio Antenna
~27 MHz; wavelength~ 36 ft
Electromagnetic Waves
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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
What Generates Electromagnetic Waves?
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Thermal radiation: Hot things glow.
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Heat causes atoms to rattle about in an object
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Atoms contain charged particles (electrons,
protons)
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Accelerating charged particles emit
electromagnetic radiation.
Other processes
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Nuclear reactions
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Magnetic fields interacting with charged
particles
Thermal Radiation
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If material is dense enough to be opaque, hot body emits
radiation in a characteristic `blackbody' spectrum
High frequency
Short wavelength
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Low frequency
Long wavelength
Hot objects emit more and at shorter wavelengths
(higher frequencies)
Line Spectra
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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
Solar Spectrum
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Central region of sun fairly
dense
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hot core
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Outer layers progressively less
dense
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Wispier outer layers
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Emits as blackbody
Line effects start
becoming noticeable
We see continuum blackbody
spectrum from the inner star
with absorption features from
the outer layers
Solar Spectrum
Calcium
Sodium
Hydrogen
Oxygen Molecules
The Sun throughout the spectrum
The Galaxy throughout the spectrum
Doppler Shift in Light
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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)
Doppler Shift in Light
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Effect is fairly modest, but spectra can be
measured very accurately
Astronomers can measure velocities
towards/away very precisely
The Drake Equation
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Drake Equation structured the class until now
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Astronomy
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Number of stars in galaxy
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Number of suitable stars
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Number of stars that form planets
Geophysics
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Number of planets suitable for life
Biology
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Where and low life forms on those planets
Spiral Galaxies
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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
Elliptical Galaxies
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Spheroidal
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Featureless
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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
Galaxies moving away from us!
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Once `spiral nebulae’
were established as
galaxies, Hubble
examined their redshifts,
and distances
Found that galaxies were
all moving away from us;
faster
Expanding Universe
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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’
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Big Bang
The Microwave background
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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!
`Big Bang’ Nucleosynthesis
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Can also predict what nuclei are formed at such temperatures
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Too cold: can’t form nuclei
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Too hot: large nuclei are torn apart
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Prediction: Universe should be mostly Hydrogen, Helium, some
Lithium: Prediction agrees with observation
Stellar Cycle
Gas Clouds
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Two broad types of clouds:
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Gas clouds
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Warm
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Very wispy
Molecular clouds
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Colder
Much denser
Gas has condensed
enough that complex
molecules have formed
Molecular Clouds
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Because molecular clouds are cooler and denser, atoms
collide more often
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Can form complex molecules
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Greatly helped by presence of grains
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Provides sites for atoms to latch onto
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Region of high atom density; atoms more easily find
other atoms to interact with
Gas Clouds
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All of these gas clouds are turbulent
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Random motions, eddies
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Where fluid comes together, dense
regions
Fluid is moving fast enough that
can compress very dense spots
Gas Clouds
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Gravity acts to try to pull
these dense spots together
However,
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Pressure in gas clouds
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Rotation
Gas Clouds
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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
Protoplanetary
Disks
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These protoplanetary
disks can be seen around
very young protostars
Protoplanetary Disks
Summary
Failed Stars
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`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
Hydrostatic Equilibrium
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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
Nuclear Reactions
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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
Given that burning is stable,
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What effects how hot a star is?
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MASS
The bigger the star that forms from the
collapse
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More pressure on the central region
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More burning
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Hotter
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Brighter
What color are more massive stars?
HR diagram and Main Sequence
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From previous, expect that
hotter stars should be brighter
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Blackbody
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More massive -> bigger
Even more than this; bigger ->
more temperature in core ->
more burning
When temperature vs brightness
is plotted, see `Main Sequence'
Other populated regions show
later stages in stellar evolution
Stellar Evolution
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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'
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Outer regions cool, redden
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Red Giant (Sun: 1 billion years)
Stellar Evolution
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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
Low Mass stars: envelope ejection
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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
High Mass Stars: Continue Burning
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Slightly more massive stars (4
to 8 solar masses):
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Everything happens faster
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Carbon can burn, as well;
one more stage of burning
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Then again leave (larger)
white dwarf and planetary
nebula behind
Type II Supernova
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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
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Heavy elements from burning
blown into surrounding gas
Type Ia Supernova
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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
Supernova Feedback
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Originally, gas was all hydrogen and helium
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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
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New stars are formed
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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
Supermassive stars
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Newly discovered:
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LBV 1806-20
150x as massive as Sun
4- to 20-million times as bright
as sun
Supermassive stars
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Question:
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If 150x as massive,
10million times as bright
as Sun, how long will it
last?
Supermassive stars
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Question:
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If 150x as massive,
10million times as bright
as Sun, how far away
does planet need to be to
have Earth-like
conditions?
Abundance of Elements
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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.
Building Blocks of Life
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These machinery of life is made of polymers
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Built out of chains of simpler molecules
(monomers)
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`modular'
Three important polymers in Earth's biology:
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Proteins
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DNA
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Building blocks for everything
Repository of genetic information
RNA
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Takes information from DNA, builds proteins
Things are Very Different when
you're a Molecule
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Gravity is not so important
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Electrical, molecular forces are
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WATER
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Constantly jostled by water molecules
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Some parts of molecules attracted to water
(hydrophilic)
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Some parts repelled (hydrophobic)
Molecules behave like little machines that are
pushed around by electrical forces
Proteins
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Proteins are long strings of
amino acids
The strings fold into
complex shapes as they form
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Buffeted by water
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Bonds linking one part
of chain to the other
Proteins
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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
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Maltose fits into `active site'
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Lock-and-key
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E. Coli has ~1000 different
proteins
Amino Acids
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tyrosine
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alanine
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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
Nucleic Acids
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(RNA only) (DNA only)
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
Nucleotides
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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
DNA
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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
DNA
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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.
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Each 3 `letter' sequence gets
translated into a single
amino acid
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64 possible 3-letter
sequences; 20 amino acids
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Some acids have several
translations
Reproduction
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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
Earth's Formation
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Condensed out of solar disk
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Small pieces (planetesimals) merging together
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Very hot – radioactive materials, collisions
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Ultraviolet radiation from sun (no protecting
ozone)
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Photodissociation
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Crust takes a long time to form
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Very geothermally active
Atmosphere
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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 (lateaccreting material) are vaporized
Volatile elements (lightest and easiest to
vaporize) can most easily diffuse away
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Hydrogen, carbon, nitrogen, oxygen
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Free hydrogen most easily evaporated
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Photodissociation breaks up molecules
Evolution of Atmosphere
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As hydrogen leaves, ozone can form
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Less hydrogen to suck up free oxygen into
water
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Cuts down ultraviolet light, photodissociation
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Atmosphere begins to stabilize
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Water vapor
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Carbon Dioxide
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Nitrogen
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Carbon Monoxide
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Very little Oxygen
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Even less Ozone
Miller-Urey Experiment
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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!
Marks – Reading Quizzes and Assignments
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Reading Quiz:
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0 NCR, 4 NCR+, 7 CR, 8 CR+, 0 CR++
Assignments:
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0 NCR, 0 NCR+, 4 CR, 9 CR+, 1 CR++
Exponential Growth
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Such growth is said to be
exponential, or geometric.
Once the process is
exponential, everything is
exponential:
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Number of children
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Number of reproductions
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Amount of area/resources
needed
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Rate of growth
Anything with a fixed
`doubling time' is exponential
Exponential Growth
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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
Exponential Growth
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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?
Exponential Growth
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Everything is exponential
By generation 20, already
expect ~20 mutations
That too is exponentially
increasing
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By generation 25, > 600
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By generation 30, > 20000
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Dividing by 100,000 just
means it takes a little longer
before it takes off
Tree of Life
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Phylogenetic tree
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`Family Tree' of species
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Distance from neighbors, root
indicates how genetically different
Three distinct branches:
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Archaea (includes
`extremophiles)
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Bacteria
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Eukaryotes (includes all life
visible to naked eye)
Building a Phylogenetic Tree
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Inferred ancestor
Evolution Time
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Inferred ancestor
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Genetic Distance
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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
Virus
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Not Included
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Self-replicating DNA or RNA
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Not self sufficient
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Requires the mechanisms of a living cell
to propagate it
As a result, much smaller than bacteria
(largest virus ~ smallest bacteria)
Virus
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Alive?
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Inert RNA/DNA/protein until
collides with target cell
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Incapable of independent action,
growth, reproduction
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Not generally considered to be
living.
Prokaryotes
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Simplest form of life
Includes bacteria (like E. Coli)
and archaebacteria
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No complex internal structure
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DNA lies together in a blob
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Prokaryotic DNA consists of one
ring
Processes occur throughout cell
Many reproduce by cell division
(asexual)
Extremophiles
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M. Jannaschii thrives near
underwater volcanic vents in
temperatures, pressures, darkness,
and lack of oxygen that would kill
other life
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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
Photosynthesis
6 H2O + 6 CO2 -> C6H12O6 + 6 O2
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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
Eukaryotes
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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
Sexual Reproduction
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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.
Cambrian Explosion
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Soon after the arrival of
eukaryotes on the scene,
there was a huge explosion
of species
Cambrian Explosion
Exponential growth -> one
expects this, but before
sexual reproduction,
evolution occurred much
more slowly
Multicellular life
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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 (?)
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Blue-Green Algae
Next Week
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Reading: Chapter 11, 12
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Brief History of Solar System
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Examination of Venus
Guest lecturer: Andrew Puckett, University of Chicago