handouts - 3-1. The first atmosphere was probably thick...

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3-1. The first atmosphere was probably thick with water vapor, along with various compounds released by volcanic eruptions, including nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen and hydrogen sulfide; however, as earth cooled, the water vapor condensed into oceans, and much of the hydrogen quickly escaped into space. 3-2. In 1953, Stanley Miller and Harold Urey, of the University of Chicago, tested the Oparin-Haldane hypothesis (organic compounds formed from simple molecules) by created a laboratory conditions comparable to those that scientists at the time thought existed on early earth. THE SET-UP A warmed flask of water simulated the primeval sea. The strongly reducing “atmosphere” in the system consisted of hydrogen, methane, ammonia, and water vapor. Sparks were discharged in the atmosphere to mimic lightning, A condenser cooled the atmosphere, raining water and dissolved compounds into the miniature sea. RESULTS As material circulated through the apparatus, Miller and Urey periodically collected sample for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms,. They also found many other amino acids and complex oily hydrocarbons. CONCLUSION Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere. 3-3. Chemical evolution (during pre-biotic times) began with simple molecules reacting with others, eventually forming more and more complex molecules. Some form of energy was needed to drive unfavorable reactions, or to aid in driving favorable reactions. Solar energy (UV light) is the most obvious source. On early Earth, there would have been no ozone layer to protect cells. UV light would split an O 2 molecule ( photolysis ), which would then form oxygen radicals that can react with other O 2 molecules to form ozone (O 3 ). UV light not only splits oxygen gas molecules, but can split other molecules as well, and so can drive unfavorable chemical reactions. UV would have been quite abundant early on, providing an energy source during chemical evolution. There are other sources of energy, such as electric discharge (i.e. lightening) and nuclear energy. Today we know that lightening can fix nitrogen gas into a solid form. 3-4. Small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water, The hydrophobic molecules in the mixture organic into a bilayer at the surface of the droplet, much like the lipid bilayer of a plasma membrane. 3-5. 3-6. 3-7. In order to have a molecular system of heredity, we need molecules that can replicate and store information. 3-8.
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handouts - 3-1. The first atmosphere was probably thick...

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