Lab 6   30 points                                                   Name: __________________

Due Date: Monday April 8 (Hand in before class)                             Lab:  M  W   1   2

Late assignments will be docked 5 points each day late.

This assignment covers some of the important concepts from Chapter 9. Short answers are acceptable for many of the questions. For questions marked with “*”, please answer using complete sentences and correct grammar. This assignment will be posted on the web later today so you can copy and paste it into word, if you like.

Chapter 9  The Chemical Environment: Evolution of the atmosphere

1.  Describe the three theories on the origin of life given in the test.*  Which explanation seems most plausible to you and why?* (4 points)

2. Geologic Evidence of the Rise of Oxygen (18 points)

a. What are the three oxidation states of iron?
b. Which state is soluble in water?
c. What happens when the soluble form of iron is exposed to oxygen?*
d. What three minerals are found in BIFs?
e. Where in the ocean did BIFs form?  How do we know this?*
f. Why can we “safely conclude that the deep oceans must have been anoxic prior to 1.9 billion years ago, during the time that BIFs formed”?*  What does BIF formation imply about atmospheric oxygen level?*
g. What form of uranium is soluble in water?
h. What is uraninite? What ion forms it?
i. You have one sedimentary rock that is 3 billion years old and another that is 1.1 billion years old.  How do the uranium components in the two rocks differ?*
j. How was the weathering of pyrite different prior to 2.2 billion years ago than it is today?*
k. Paleosols older than 2.2 billion years have lost significant amounts of iron compared to younger (<1.9 billion year old) palesols. Explain why this is so.*
l. What are redbeds? Where do they form?
m. What do redbeds indicate?*
n. To summarize this section, what geological evidence do we have for the rise of oxygen? (Be concise.)

Figure 9-15 (8 points)

a. What does the graph suggest about CO2 levels over earth’s history?*
b. Why do the delta13C differ for carbonates and organic carbon?*
c. How are O2 and CO2 atmospheric levels linked?*
d. When did cyanobacteria start producing oxygen? When did atmospheric oxygen become apparent? What are the various explanations for the delayed rise in oxygen levels?*

Please proofread and edit your work. Make sure your name is on the typed pages.