Q25.3-1CC - Campbell Biology

Question

The first appearance of free oxygen in the atmosphere likely triggered a massive wave of extinctions among the prokaryotes of the time. Why?

Step-by-Step Solution

Answer

The free oxygenated atmosphere has triggered massive extinctions among the prokaryotes of the time due to the free oxygen attacking chemical bonds, stopping the working of enzymes, and deteriorating cells. 

Step 1: Prokaryotes

Prokaryotes are facultatively anaerobic and expanded in an anaerobic environment. They would have been negatively influenced by oxygenation in the atmosphere. The Earth’s massive mass extinction was caused by the building of oxygen in the environment that destroyed anaerobic bacteria.

Step 2: Cyanobacteria

Cyanobacteria belong to Gram-negative bacteria, photosynthetic organisms found in the aquatic environment that produce oxygen as a waste product. They can multiply rapidly and convert sunlight into energy through the process of photosynthesis. 

The pre-historic Earth had no free oxygen, and the reduction of abundant oxygen damaged ninety percent of all life forms on Earth.

Step 3: Photosynthesis and the oxygen revolution

The photosynthetic prokaryotes have evolved oxygenic photosynthesis, and the appearance of free oxygen is found to be dissolved in the surrounding water. The free oxygen reacted with Fe when it reached a high concentration to cause iron precipitation as iron oxide and collected as sediments in the Earth.

The massive extinctions occurred among the prokaryotes of the time by the appearance of free oxygen because free oxygen attacks chemical bonds. Moreover, it prevents enzymes from functioning. It also destroys cells. The Great Oxygen Event occurred when a high concentration took place in the atmosphere and the shallow ocean during the Paleoproterozoic era.