Lecture 14. Source of Organic compounds, Miller-Urey Experiment

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Lecture 14. Source of Organic compounds,
Miller-Urey Experiment
reading Chapter 5
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The Process of Interplanetary Transfer

• Origin of life has to occur SOMEWHERE
• Have to get the organisms off the moon or planet
• only real way impacts
• 3. The organisms have to survive the trip
  through space

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The Process of Interplanetary Transfer, cont.

• Organisms in space have to survive impact onto
  new body
• Several Aspects
• - heating
• - acceleration
• - size of meteorite
• small burst in atmosphere and burn up
• larger outer surface melts, forms a fusion
  crust
• very large impactor melts or vaporizes upon
  impact
• - impactor has to break up to release the
  organisms
• Organisms have to survive, grow, and reproduce.
  Have
• to find an optimal environment.

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Is Panspermia common or rare now? Has life been
transferred once or twice? Have their been many
origins of life on other parent bodies?
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Organic Carbon in the Universe
Abundant in various forms in dark interstellar
clouds. Visible light doesnt pass through, but
infrared light does. Molecules in
diffuse clouds do not emit visible light (cold,
50K). Radiate low energy photons due to
rotational, vibrational energies. Radio
telescopes in microwave and millimeter-wave
frequencies Detect small and medium-sized
molecules. Detect energy given off as precise
bands of energy. Each compound gives off
characteristic patterns.
Molecular cloud Barnard 68
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Example Radio Spectrum
millimeter-wavelength spectrum of the core of the
Orion giant molecular cloud, Owens Valley Radio
Observatory
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Over 70 Interstellar Molecules are Known
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Types of Environments
Giant Molecular Clouds Orion Molecular Cloud one
of the most important - site of active star
formation Cold Molecular Clouds Many small
clouds are known TMC1 (Taurus Molecular Cloud
1) Large abundance of C compounds Cool Carbon
Stars Carbon-rich red giants IRC10216
dense shell of dust and gas rapidly
expanding shell R Coronae Borealis releasing
puffs of dust at intervals causing periodic
brightness
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Polyynes
Easily seen by microwave telescopes H-C?N cyanid
e H-C?C-C?N H-C?C-C?C-C?N cyanobutadiyne
as the chain length increases, abundance
decreases, although chains of C33 are seen in the
interstellar medium.
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Polycyclic Aromatic Hydrocarbons
Planar rings of carbon. Single forms benzene,
naphthalene, pyrene. Very stable family or
organic compounds. Detected using infrared
telescopes - have characteristic emissions
at micrometer wavelengths. Also anthroprogenic -
soot.
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Buckyballs
Evidence for large aggregates of C in conditions
mimicking C stars. C60 is abundant because it is
extremely stable. Called buckminsterfullerene
after designer of geodetic domes. Form
spontaneously - to curl mix pentagons and
hexagons.
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Extraterrestrial Sources of Organic Carbon
Are a number of sources of organic compounds on
the early Earth - comets - meteorites -
interplanetary dust - lightning - abiotic
synthesis in hydrothermal systems
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Comets
NASAs Deep Impact 820-pound copper impactor hit
Comet Tempel 1 July 4, 2005 at 23,000
mph. density of comet very low - porosity high
(crumbly texture) hit obliquely, never really
hit a solid layer 70-80 is empty
space abundant craters on the surface giant
plume of gas and dust far richer in carbon
compounds 5500 tons of water thrown into
space other ices carbon dioxide (CO2), carbon
monoxide (CO), ammonia (NH3) greater quantities
of dust that contained HCN, methyl
cyanide acetylene, formaldehyde other
unidentified organic compounds
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Meteorites
Carbonaceous chondrites Rare type of stony
meteorite, only 100 known. Primitive, unaltered
(never heated above 50C) Elemental composition
similar to the nebula. Contain large amounts of
Mg-rich silicate minerals (olivine,
serpentine) iron oxides and sulfides. Contain
water (up to 20). 3 organic compounds PAHs am
ino acids Murchison meteorite 1969 fell on
Australia. Has gt 230 amino acids. Vigarano
meteorite Fell in 1910. Contains CAIs -
Calcium-aluminum inclusions. The most ancient
minerals known.
contain chondrules - oldest objects in the solar
system. Melted droplets of silicates that
solidified in the solar nebula
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Sugars Alcohols found in Murchison Murray
Meteorites
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Interplanetary Dust Particles
Most come from ground up meteorites and
comets. Some are presolar- made in giant
supernovae explosions and in outer shells of red
giants - older than the age of the universe -
easily identified because H, O, and N isotopes
are very different Also 3 organic C (aliphatic
and aromatic - PAHs) Are so small they dont heat
up much in the atmosphere 1 sec _at_ 500C
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Abiotic Synthesis - The Miller-Urey Experiment
A.I. Oparins Book In a strongly reducing
atmosphere of the early Earth, inorganic
molecules would spontaneously form organic
molecules (simple sugars and amino acids). These
would then react, form primitive cells. The
experiments were done in Harold Urey's lab when
I was a graduate student. Urey gave a lecture in
October of 1951 when I first arrived at Chicago
and suggested that someone do these experiments.
So I went to him and said, "I'd like to do those
experiments". The first thing he tried to do was
talk me out of it. Then he realized I was
determined. He said the problem was that it was
really a very risky experiment and probably
wouldn't work, and he was responsible that I get
a degree in three years or so. So we agreed to
give it six months or a year. If it worked out
fine, if not, on to something else. As it turned
out I got some results in a matter of
weeks. interview by Sean Henahan, 1996
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The Miller-Urey Experiment
Started with a reducing atmosphere - H2, CH4,
NH3 Overnight - trarry brown goo. One week -
10-15 of the C now organic compounds. 4 of that
simple amino acids. Conclusion amino acids can
form spontaneously.
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The Miller-Urey Experiment, cont.
We now think the early atmosphere was not
reducing, but was more oxidizing CO2, N2. When
you do the Miller-Urey experiment with these
gases, get a much much lower yield, fewer
organic compounds. The reducing conditions work
so well because they generate HCN, which reacts
with NH3 to make amino acids. Prebiotic
chemistry Using organic chemistry relevant to
the early Earth to identify how compounds found
in cells came about. Have formed all the amino
acids. Some complex sugars (made by
polymerization of formaldehyde) Bases of nucleic
acids (not connected to sugar or phosphate) No
good way known to make fatty acids/lipids.
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Lecture 15. Prebiotic Chemistry, Pyrite, Clays,
Transition from Abiotic to Biotic World
reading Chapter 5
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Mystery of Enceladus
Cassini Spacecraft found older terrains and
major fractures on moon Enceladus Course
crystalline ice which will degrade
over time. Must be lt 1000 years old! Organic
compounds found in the fractures. Must be heated
- required T gt 100K (-173C) Erupting jets of
water observed. Cause of eruptions not known.