Transcript Lecture14

Lecture 14. Source of Organic compounds,
Miller-Urey Experiment
reading: Chapter 5
The Process of Interplanetary Transfer
1. Origin of life has to occur SOMEWHERE
2. Have to get the organisms off the moon or planet
only real way: impacts
3.
The organisms have to survive the trip through space
The Process of Interplanetary Transfer, cont.
4. 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
5. Organisms have to survive, grow, and reproduce. Have
to find an optimal environment.
Is Panspermia common or rare now?
Has life been transferred once or twice?
Have their been many origins of life on other parent bodies?
Organic Carbon in the Universe
Abundant in various forms in dark interstellar clouds.
Visible light doesn’t pass through, but infrared light does.
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Molecular cloud
Barnard 68
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.
Example Radio Spectrum
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millimeter-wavelength spectrum
of the core of the Orion giant
molecular cloud, Owens
Valley Radio Observatory
Over 70 Interstellar Molecules are Known
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
IRC+10216
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
cyanide
H-CC-CC-CN
cyanobutadiyne
H-CC-CN
as the chain length increases, abundance decreases, although chains of
C33 are seen in the interstellar medium.
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.
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.
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
Comets
NASA’s Deep Impact
820-pound copper impactor hit Comet Tempel 1
July 4, 2005 at 23,000 mph.
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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 50˚C)
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
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amino acids
Murchison meteorite:
1969 fell on Australia.
Has > 230 amino acids.
Vigarano meteorite:
Fell in 1910.
Contains CAIs - Calcium-aluminum inclusions.
The most ancient minerals known.
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contain chondrules - oldest objects
in the solar system. Melted droplets of
silicates that solidified in the solar nebula
Sugars & Alcohols found in Murchison & Murray
Meteorites
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 don’t heat up much in the atmosphere
1 sec @ 500˚C
Abiotic Synthesis - The Miller-Urey Experiment
A.I. Oparin’s 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
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.
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.
Lecture 15. Prebiotic Chemistry, Pyrite, Clays,
Transition from Abiotic to Biotic World
reading: Chapter 5
Mystery of Enceladus
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Cassini Spacecraft found older terrains
and major fractures on moon Enceladus
Course crystalline ice which will degrade over
time.
Must be < 1000 years old!
Organic compounds found in the fractures.
Must be heated - required T > 100K (-173˚C)
Erupting jets of water observed.
Cause of eruptions not known….
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