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CHAPTER 19 O RIGIN AND H ISTORY OF L IFE Chapter Outline 19.1 Origin of Life A. Chemical evolution is the increase in complexity of chemicals that led to the first cells. 1. Today, life only comes from life. 2. However, the first cells had to arise from an increased complexity of chemicals. B. The Primitive Earth 1. The earth came into being about 4.6 billion years ago. 2. Heat from gravitation and radioactivity formed the earth in several layers with iron and nickel in a liquid core, silicate minerals in a semi-liquid mantle, and upwellings of volcanic lava forming the first crust. 3. The earth’s size provides a gravitational field strong enough to hold an atmosphere. 4. Earth’s primitive atmosphere differed from current atmosphere, consisting of: a. water vapor (H 2 O), b. nitrogen (N 2 ), c. carbon dioxide (CO 2 ), d. small amounts of hydrogen (H 2 ), and e. carbon monoxide (CO). 5. Primitive atmosphere was formed by volcanic out-gassing characteristic of the young earth. 6. The primitive atmosphere contained little free oxygen (O 2 ) and was probably a reducing atmosphere as opposed to the oxidizing atmosphere of today. a. A reducing atmosphere lacks free O 2 and allows formation of complex organic molecules. b. An oxidizing atmosphere contains free O 2 and inhibits formation of complex organic molecules. 7. The earth was so hot that H 2 O only existed as a vapor in dense, thick clouds. 8. As the earth cooled, H 2 O vapor condensed to form liquid H 2 O, and rain collected in oceans. 9. The earth’s distance from the sun allows H 2 O to exist in all phases: solid, liquid, and gas. 10. NASA photos seem to confirm that earth is bombarded by comets adding substantial water vapor. C. Monomers Evolve 1. Larger comets and meteorites have pelted the earth perhaps carrying organic chemicals. 2. A meteorite from Mars (ALH84001) landed on earth 13,000 years ago; may have fossilized bacteria. 3. Aleksandr Oparin’s 1938 Hypothesis a. Oparin suggested organic molecules could be formed in the presence of outside energy sources using: 1) methane (CH 4 ) 2) ammonia (NH 3 ) 3) hydrogen (H 2 ) 4) water (H 2 O) b. Experiments performed by Stanley Miller and others show these gases in the primitive atmosphere reacted with one another to produce small organic molecules. 4. Lack of oxidation and decay allowed organic molecules to form a thick, warm organic soup. 5. Ammonia may have been scarce; undersea thermal vents however produce much ammonia and additional natural reactions form peptides. D. Polymers Evolve 1. Newly formed organic molecules polymerized to produce larger molecules and macromolecules . a. Gunter Wachtershauser and Claudia Huber have secured peptides using iron-nickel sulfides under ventlike conditions.
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b. Such minerals have a charged surface that attracts amino acids and provides electrons so they bond together.
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This note was uploaded on 10/24/2009 for the course BIO 172 taught by Professor Clark during the Fall '08 term at University of Michigan.

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