Topic_11___Biosphere_I - Topic 11: Biosphere I - History of...

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Topic 11: Biosphere I - History of Life on Earth A. Time framework for the origin of life on Earth (geologic time scale)
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a. Age of Earth ~ 4.5 b.y. b. Liquid H 2 O by 4.0 b.y. c. Oldest preserved rocks on Earth (3.96 b.y. in Greenland) show no sign of life d. But , 3.86 b.y. rock in Greenland does show evidence of life Microfossil from Apex Chert (3.5 b.y.) Image of fossilized algal mat 3.5 b.y. B. Earliest life consists of prokaryotes (single-celled, no nuclei) a. Examples include bacteria, blue-green algae (today called " cyanobacteria ") b. Microscopic c. Could survive in environments devoid of oxygen d. The only forms of life for 2 billion years C. Origin of life in early Earth environment? a. Atmosphere i. Rich in H 2 O, H 2 , CO 2 , N 2 ii. Presence of NH 3 (ammonia) and CH 4 (methane) iii. Absence of O 2 b. Abundant H 2 O on surface, very warm, active tectonism
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c. NH 3 + CH 4 + H 2 O + H 2 + energy = amino acids (building blocks of organic compounds) Miller -Urey Experiment D. O
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This note was uploaded on 09/02/2009 for the course GEO 302C taught by Professor Yang during the Spring '08 term at University of Texas at Austin.

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Topic_11___Biosphere_I - Topic 11: Biosphere I - History of...

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