Question
Select the correct answer. How did cyanobacteria affect Earth's early atmosphere? A. They replaced oxygen with carbon dioxide in the atmosphere. B. They eliminated the harmful ultraviolet rays of the Sun. C. They replaced carbon dioxide with oxygen in the atmosphere. D. They absorbed ozone molecules from the atmosphere.
Answer
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Roland
Professional · Tutor for 6 years
Answer
C. They replaced carbon dioxide with oxygen in the atmosphere.
Explanation
Cyanobacteria, which are also known as blue-green algae, played a crucial role in shaping the Earth's early atmosphere through the process of photosynthesis. During photosynthesis, cyanobacteria use sunlight to convert carbon dioxide and water into glucose and oxygen. This process resulted in the release of oxygen into the atmosphere. Before the advent of cyanobacteria, the Earth's atmosphere had a very low concentration of oxygen. The oxygen produced by cyanobacteria began to accumulate in the atmosphere over time, leading to a significant increase in the atmospheric oxygen level. This event is known as the Great Oxidation Event. It is important to note that cyanobacteria did not replace oxygen with carbon dioxide; rather, they did the opposite. They also did not have a direct role in eliminating ultraviolet rays or absorbing ozone molecules. Instead, the oxygen they produced eventually led to the formation of the ozone layer, which helps to protect the Earth from harmful ultraviolet rays.