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SQ01_Lect_1_3.ans

SQ01_Lect_1_3.ans - BioMI 290 Study Questions#1 Lectures...

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BioMI 290 1/27/08 Study Questions #1 Lectures 1-3 (ANSWERS) These questions are to help you better understand the material presented in lecture. We will not collect your answers. The answers will be posted Monday (afternoon) to the BioMi 290 web site. Part I. The History of Life 1) Describe the conditions of early Earth 4.2 - 3.8 Ga ago as the first life was starting on Earth. What geological evidence shows that liquid water, which is essential for life to evolve, was present on Earth near the end of that time period? The Earth was very hot as a result of energy discharged from constant bombardments and volcanism. The atmosphere had no oxygen; it contained mostly CH4, N2, CO, CO2, NH3 and some H2. Water was vaporized again and again in the early part of this period, but eventually, as the bombardments eased, liquid water condensed as rain to form a global ocean. As the planet cooled further, sedimentary basins formed which are recorded as sedimentary deposits in the oldest known rock formations such as those in the Isua Formation in Greenland dating from about 3.8-3.7 Ga. 2)Describe the Miller/Urey “organic soup” experiment. The apparatus is shown in the handout Lecture 2. It consisted of a flak filled with water which was boiled in an anoxic atmosphere containing gases that were thought to be present in the early atmosphere of Earth. The atmosphere was subjected to electric discharges meant to simulate lightning as an energy source. a) What did the experiment prove about the origin of organic precursor molecules and life on early Earth? That in a mixture of CH4, NH3, H2, and water; providing an energy source ( e.g. an electric discharge or UV radiation) under anoxic conditions similar to those thought to exist in the atmosphere of early Earth , organic compounds were readily formed, including amino acids and other building blocks of macromolecules in living cells today. b) What are some problems with the “organic soup” theory? Their organic mixture contained concentrations CH4 and NH3, which some people say were not in the early atmosphere. In later experiments CO2 and N2 were added with the same results. The experiments gave no information on how polymerization of macromolecules (primarily dehydration reactions) might have occurred in the aqueous phase. c) What is an alternate hypothesis? Organic chemicals and living cells could have been brought from other habitable planets (e.g. Mars) on meteorites, which may have been a wet and warm place in those early days, and comets from outer space, which are known to contain significant amounts of water ice and organic compounds.
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