reading: chapter 5 lecture 14. source of organic compounds, miller-urey experiment

reading: Chapter 5

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

1. Origin of life has to occur SOMEWHERE

2. Have to get the organisms off the moon or planetonly real way: impacts

3. The organisms have to survive the trip through space

The Process of Interplanetary Transfer

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 uplarger: outer surface melts, forms a fusion crustvery large: impactor melts or vaporizes upon impact

- impactor has to break up to release the organisms

5. Organisms have to survive, grow, and reproduce. Haveto 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.

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.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Molecular cloudBarnard 68



millimeter-wavelength spectrumof the core of the Orion giant molecular cloud, OwensValley Radio Observatory

Example Radio Spectrum



Over 70 Interstellar Molecules are Known

Types of Environments

Giant Molecular CloudsOrion Molecular Cloud one ofthe most important - site of activestar formation

Cold Molecular CloudsMany small clouds are knownTMC1 (Taurus Molecular Cloud 1)Large abundance of C compounds

Cool Carbon StarsCarbon-rich red giantsIRC+10216 dense shell of dust and gas rapidly expanding shellR Coronae Borealis releasing puffs of dust at intervals causing periodic brightness





Polyynes

Easily seen by microwave telescopes

H-CN cyanide

H-CC-CN

H-CC-CC-CN cyanobutadiyne

as the chain length increases, abundance decreases, although chains ofC33 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 Cin conditions mimicking C stars.

C60 is abundant because it is extremelystable.

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





CometsNASA’s Deep Impact820-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 compounds5500 tons of water thrown into spaceother ices: carbon dioxide (CO2),

carbon monoxide (CO), ammonia (NH3)greater quantities of dust that contained

HCN, methyl cyanideacetylene, formaldehydeother unidentified organic compounds



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

PAHsamino 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.



contain chondrules - oldest objectsin 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 wasmore oxidizing: CO2, N2.

When you do the Miller-Urey experiment with these gases, geta much much lower yield, fewer organic compounds.

The reducing conditions work so well because they generateHCN, which reacts with NH3 to make amino acids.

Prebiotic chemistry:Using organic chemistry relevant to the early Earth to identifyhow 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.

reading: Chapter 5

Lecture 15. Prebiotic Chemistry, Pyrite, Clays, Transition from Abiotic to Biotic World



Cassini Spacecraft found older terrainsand major fractures on moon Enceladus

Course crystalline ice which will degrade overtime.

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….



Mystery of Enceladus



reading: chapter 5 lecture 14. source of organic compounds, miller-urey experiment

Documents

molecular cloudbarnard

interstellar molecules

source of organic compounds

orion giant molecular

interplanetary dust

carbon dioxide co2

radio telescopes

interstellar medium