| 1) | Why are mass extinctions important events in earth's history? | 
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| 2) | Name two groups which died off at the Cretaceous-Tertiary boundary | 
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| 3) | List two controls on phytoplankton productivity in the earth's oceans | 
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|  | A) What events could trigger a decrease in phytoplankton productivity? | 
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| 4) | Match the mass extinction with its result | 
	|  | | A. Cambrian-Ordovician (510 MY) B. Permian-Triassic (245 MY)
 C. Triassic-Jurassic (208 MY)
 D. Cretaceous-Tertiary (65 MY)
 
 | 1. ammonites become extinct 2. 2/3 of existing trilobites extinct
 3. radiation by dinosaurs
 4. 90% of fossil life forms become extinct
 
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| 5) | How can sea floor spreading rates affect sea level? | 
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