Download Ch18 Life - UCF Physics

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Astronomical spectroscopy wikipedia, lookup

Microplasma wikipedia, lookup

Stellar evolution wikipedia, lookup

Planetary nebula wikipedia, lookup

Star formation wikipedia, lookup

Main sequence wikipedia, lookup

Standard solar model wikipedia, lookup

Transcript
Life
Start with the Early Earth…
• Hot ~ 230C
• Oceans (at about 4.2 By)
• CO2 atmosphere with ammonia,
methane, water vapor, and nitrogen
• Lots of UV-radiation (no ozone)
• Reducing conditions
• Lots of lightning
Miller-Urey Experiment
• Idea was that conditions
on the primitive Earth
could produce chemical
reactions that made
organic compounds from
inorganic material.
• Used water (H2O),
methane (CH4), ammonia
(NH3), and hydrogen (H2)
• Made up to 22 different
amino acids
• After a week about 10–
15% of the carbon within
the system was now in
the form of organic
compounds
So we have organics….
• Turns out that there are
lots of other possible
origins for organics
molecules
– Deep sea vents
– Spontaneous formation of
peptides
– Radioactive beaches
– And many, many more…
• Now you need to make
cells….
• There are, of course,
piles of theories on the
origin of cells
–
–
–
–
Clays
Lipids
Polyphosphates
PAHs
PAHs: Self Organizing Building
Blocks?
• Polycyclic Aromatic
Hydrocarbons (PAHs) are
amphiphilic (they have parts
that are both hydrophilic
and hydrophobic).
• In solution, they tend to self
organize themselves in
stacks, with the
hydrophobic parts
protected.
• In this self ordering stack,
the separation between
rings is 0.34 nm, the same
separation found in RNA
and DNA.
• Smaller molecules will
naturally attach themselves
to the PAH rings.
However it happened…
• We think prokaryote cells
(single-cell organisms that
lack a nucleus) developed
as early as ~ 3.85 Billion
years ago
• WE KNOW that by 3.5 Billion
years ago we had bacteria
and blue-green algae
• By 2 Billion years ago we
had eukaryotes (organism
whose cells have a nucleus)
• By 1 Billion years ago we
had multicellular life
• By 600 million years ago we
had simple animals
By 2.5 Billion years ago plankton were
altering the oxygen content of the atmosphere
What are the requirements for Life
• Liquid Water
– Too close….water boils off
– Too far….water freezes
• A source of Energy
– Solar
– Tidal
• Available Organic Molecules
– Carbon Compounds….abundant in comets and some
asteroids
• Enough Time
– A stable environment
– Evolve Complexity
• This comes together in the concept of a Habitable
Zone
But there are a few other things…
•
•
•
•
•
•
Stable Sun
Near-circular planetary orbits
Earth-like planetary mass
Night and Day
No major orbital disruptions
Occasional mass extinctions are OK
– But not too often….
Galactic Habitable Zones
• It is all about stability
• If it takes stability for over 4 billion years
to develop intelligent life, you need to
be in the Galactic suburbs
• Stay away from
–
–
–
–
Black holes
High star density areas (comets)
Star forming regions
Supernova
• For a start, stay away from the Galactic
center
Metallicity
• No planets have been found around stars
with less than 40% of the Sun’s metal ratio
• Too high metallicity is also a problem (we
think…..)
– Tend to larger, more volatile-rich, lower-relief
– Water-covered
– Easier to form gas-giants…could be bad for
terrestrial Planets
• Metallicity increases steadily toward the
Galactic center
– More matter, faster star formation
Co-rotation
• Another thing to avoid is
transiting spiral arms
• These are areas of high
stellar density and high
star formation
– Increases probability of
close gravitational
encounters
– Or being to close to
Supernova
• Our Sun’s galactic orbital
period is about the same
as rotation period the
nearby spiral arm
The Drake Equation
• R*Fp*Ne*Fl*Fi*Fc*L = N
– R = The number of suitable stars, effectively F, G, and K stars,
that form in our galaxy per year (about 1)
– Fp= The fraction of these stars that have planets (about 0.5)
– Ne = The number of Earth-like planets (planets with liquid water)
within each planetary system (we are learning about this
now…..expect an answer in 3-5 years)
– Fl = The fraction of Earth-like planets where life develops (we
could have some idea in 20 years)
– Fi = The fraction of life sites where intelligent life develops (how
are we ever going to know this?)
– Fc = The fraction of intelligent life sites where communication
develops (one would do….)
– L = "The "lifetime" (in years) of a communicative civilization
(how long have we been a communicative civilization?)
– N = The number of communicative civilizations within the Milky
Way today
The Drake Equation
• R*Fp*Ne*Fl*Fi*Fc*L = N
• Drake thinks that N is about 10,000
for our Galaxy.
• I really doubt that…..
– Throw into the equation the limitations
of metallicity, local star density, near-by
supernova, and binary systems
• But a few would not be unreasonable
How can we tell if there is life?
• Look at the
atmosphere….
• Life uses the
atmosphere as a
source of energy and
a sink for waste
products.
• We should know
about nearby
systems in ~20 years
But we haven’t we found any
communicative civilizations
• Well….….there may be nothing to find.
• Think about it…..how would an
advanced civilization communicate?
– How long has it been since Marconi
invented radio?
– Transatlantic commercial service was
established in 1907
Big Questions…
• Is there life elsewhere in our solar
system?
– There is no evidence
• Is there intelligent life elsewhere
in the Universe?
– There is no evidence