Chapter 25 Group Notes

Chapter 25 Group Notes - Chapter 25 - The H istory of Life...

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Chapter 25 - The History of Life on Earth Overview A. Past organisms were different from those now alive. B. The fossil record shows macroevolutionary changes over large time scales including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time. II. 25.1 - Conditions on early Earth made the origin of life possible A. Earliest evidence of life comes from fossil records of microorganisms about 3.5 billion years ago. B. Observations and experiment have lead scientist to a hypothesis on how life began: i. Abiotic synthesis of small organic molecules, such as amino acids and nucleotides ii. Joining of these small molecules into macromolecules. iii. The packaging of these molecules into protobionts, that allowed a different chemistry within the cell that was different from its surrounding chemistry. iv. Origin of self replicating molecules that made inheritance possible. C. Earth formed about 4.6 billion years ago, along with the rest of the solar system. i. Early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, and hydrogen sulfide) ii. Oparin and Haldane hypothesized that the early atmosphere was a reducing environment. - with the thought that organic molecules were yielded in a reducing environment iii. Miller and Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible. - By duplicating what they expected Earth's early atmosphere to be like they were able to create organic molecules and forms of amino acids. iv. However, evidence is not yet convincing that the early atmosphere was reducing. - The atmosphere may have been reducing in certain pockets near deep sea vents and submerged volcanoes v. Hypothesis also supported by the findings of amino acids in meteorites - Amino acids are the building blocks of proteins and are a necessity for the beginning of life. D. Abiotic Synthesis of Macromolecules Dripping solutions of amino acids onto hot sand, clay, or rocks, produces amino acid polymers. - These polymers may have acted as weak catalysts for a variety of reactions on earth.
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- Furthermore, these polymers helped in the creation of macromolecules. E. Protobionts - aggregates of abiotically produced molecules surrounded by a membrane like structure (in "English"=abiotic structures surrounded by membrane ) i. These structures provided the necessary conditions for nucleotides to form. (combining macromolecules) ii. Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment . - Replication and metabolism are key properties of life. iii. Experiments demonstrate that protobionts could have formed spontaneously from
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This note was uploaded on 01/25/2011 for the course BIO 1510 taught by Professor Unknown during the Spring '07 term at Georgia Tech.

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Chapter 25 Group Notes - Chapter 25 - The H istory of Life...

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