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homework6_ans - SIO 10 Winter 2009 Homework#6 Due...

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SIO 10 – Winter 2009 Homework #6 Due Monday, February 23, 2009 (NOTE THE EXTRA TIME) Lectures 16, 17, 18 (Chapters 13, 14, 15) 20 points Write your answers on a separate sheet of paper with your name and student ID on it. Short, concise answers are preferred above lengthy ones. Note that your handwriting must be legible to receive credit. Be sure to answer all sub-questions. 1) The early atmosphere appears to have been low in oxygen, but today the atmosphere is made up of about 20% oxygen. a) What are Redbeds? (1 pt) b) How do Redbeds help indicate the timing of this switch to an oxygen-rich atmosphere? (1 pt) c) What are stromatolites? and how did they contribute to the switch to an oxygen- rich atmosphere? (2 pts) a) Redbeds are sedimentary rocks with abundant oxidized iron, which only form in the presence of oxygen. b) Redbeds only appear after 2.2 Ga in the rock record. c) Stromatolites are mounds of photosynthetic bacteria. Since photosynthesis produces oxygen, the evolution of stromatolites helped add oxygen to the atmosphere.
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