SAT Subject Biology Practice Question 244: Answer and Explanation

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Question: 244

14. Some rocks feature red bands or streaks made up of iron oxides, formed when iron reacts with oxygen. These originated from dissolved iron in the oceans, which formed oxides and settled to the ocean bottom. What allowed this chemical and physical process to occur?

A. Early reducing atmosphere of Earth
B. Evolution of cyanobacteria
C. Symbiosis of photosynthetic bacteria and protists
D. Adaptation of plants to terrestrial environments
E. Metabolic activity of the first heterotrophs

Correct Answer: B

Explanation:

The evolution of cyanobacteria, the first oxygen-releasing photosynthetic organisms, led to the accumulation of oxygen in Earth's surface waters and atmosphere. The oxygen reacted with dissolved iron, creating the oxides found in rocks.

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