Download Lecture 1: Life: How common? What is it? How can we find it?

Lecture 1: Life: How common? What is
it? How can we find it?
• Takeaway messages:
–
–
–
–
Microbial life probably widespread
More advanced life not so certain
No definite proof as yet
Difficult to define what it means to be
alive
Life on originated very early on
• 3.5-4.0 BYA
• Impacts could have been frequent
• Life may have originated more than
once
• Inevitable, given the right conditions?
Right conditions are common
• Basic for Life As We Know It:
– Liquid Water
– Concentrated supply of organic material
– Appropriate energy source
• Water fairly abundant; need to be properly
placed relative to star
• C, H, O, N, P, S all relatively abundant
• Large fraction of stars in the Galaxy provide
steady, long-lived source of energy
Life can thrive in forbidding
environments
• Microbial life found in:
– Hot springs, hydrothermal vents on
ocean floor, in salty, alkaline, or acid
solutions
– Even in radioactive waste dumps!
• Extremophiles tell us that life can
thrive, maybe originate in places than
we used to think impossible
Yellowstone Hot Spring
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Complex organic molecules
found all over the Galaxy
• Radio astronomers (1950-today) have
found > 100 molecules in interstellar
space
• Comets, meteorites even larger inventory
– Include fundmental building blocks of life
– Murchison & other meteorites: amino acids,
nucleotides, sugars
Molecular clouds
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Molecules with Two Atoms
H2 hydrogen
CSi carbon monosilicide
CS carbon monosulfide
NS nitrogen monosulfide
HCl hydrogen chloride
KCl potassium chloride
AlF alum’m monofluoride
SiN silicon mononitride
SiS silicon monosulfide
OHhydroxyl radical
CN cyanide radical
CO+SO+ CH CH+
CO carbon monoxide
CP carbon monophosphide
NO nitric oxide
SO sulfur monoxide
NaCl sodium chloride
AlClaluminum monochloride
PN phosphorus mononitride
SiO silicon monoxide
NH imidyl radical
C2diatomic carbon
HFhydrogen fluoride
Molecules with Seven Atoms
CH3C2H methylacetylene
CH3NH2 methylamine
HC4CN cyanobutadiyne
CH3CHO acetaldehyde
CH2CHCN acrylonitrile
C6H
Molecules with Nine Atoms
CH3)2O dimethyl ether
C2H5CN ethylcyanide
C2H5OH ethanol
CH3C4H methylbutadiyne
Molecules with Nine Atoms
(CH3)2CO acetone
CH3C4N?cyanomethylbutadiyne
NH2CH2COOH? aminoacetic acid
Seeding of life from planet
to planet
• Martian meteorites found on Earth
– Kicked off by impacts, captured by Earth
• Study of meteorites + analysis shows
primitive organisms could survive
• Once started on one planet, life could
spread to all hospitable environments
in that planetary system
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Many, even most stars have
planets (we think)
• Natural result of star formation
• Protoplanetary disks common around
young stars, protostars
• Debris disks seen around more
mature stars
• Astronomers (UCB, etc) have found
many (200 +) planets already
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Lots of stars --> Lots of planets
• 10,000,000,000 stars in Milky Way
• 10,000,000,000 galaxies in known U.
• 10--followed by 19 0’s = number of
stars in the U.
• Even if a tiny fraction have planets,
that’s a LOT of planets
Life commonplace in U.
• Given right conditions, life inevitable ,
right conditions found everywhere,
life can live in much more hostile
environments than we
thought,complex organic molecules
easily formed, planets are abundant
• So if we look, we’ll find it (eventually)
New field: Astrobiology
• What are the general conditions
needed for life to appear?
• How common is it (really)?
• Where will we find it, and how?
• What will it be like?
• HOLY GRAIL: Find SOMETHING
biogenic and NOT from Earth
What does “alive” mean?
• Tough question. So far has eluded the best
of them.
• Is it like pornography: Can’t define it, but
you know it when you see it?
– Doesn’t that beg the question??
• Self-replicating? Not enough.
• Most will agree: to be alive a system must
EVOLVE to adapt to its environment.
• Darwinian evolution --> Self-replication,
selection, mutation
How about digital life?
• The Ancestor: 80 byte machine code
• Self-replicating
• Ancestor-->Daughters-->etc = making
copies of the genetic code
• Random mutations (1-->0 or 0-->1)
• Fitness criteria-->compete for
memory space
• Q: Is it alive??
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Tierra home page: http://www.his.atr.jp/~ray/tierra/index.html
Don’t ask what it IS, but what
it DOES?
• Life METABOLIZES: interacts with
and changes its immediate (maybe
even global) environment
• Certain substances taken in (through
membrane), energy extracted, other
chemicals exhausted
• Changes to environment can be small
and local up to massive and global
Some changes due to metabolism
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•
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Composition of the atmosphere
Alters isotopic ratios
Changes balance of enantiometers
Affects relative abundances of
organic molecules
• Even extinct organisms leave trail:
chemical, mineralogical, morphological
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Familiar example: O2 we breathe
• Earth’s atmosphere is way out of chemical
equilibrium
• All the molecular Oxygen should go away
(oxidizes) in ~ 4 Myrs
• What’s the source of replenishment?
LIFE, primarily MICROBES
• Alien scientist looking at Earth would
immediately suspect planet might be inhabited
Solar system vs extra-solar
searches
• Quite different
– Solar system searches much more
detailed, primarily local
– Looking for life outside the SS much
cruder-->look for global biomarkers
• In both cases: “follow the water”
• Both cases require big investment
Evidence for water on Mars?
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Lecture 1: Life: How common? What is
it? How can we find it?
• Takeaway messages:
–
–
–
–
Microbial life probably widespread
More advanced life not so certain
No definite proof as yet
Difficult to define what it means to be
alive