Which statement about oxygen and ancient Earth is true?

Question

Quizplus · Accepted Answer

Early bacteria, particularly cyanobacteria, generated free oxygen as a by-product of the chemical splitting of water through photosynthesis. This process gradually increased the concentration of oxygen in the atmosphere. The other options are incorrect. The atmosphere of early Earth had very little free oxygen, and it was only after the emergence of photosynthetic cyanobacteria that oxygen began to accumulate. Cyanobacteria are still present in modern times and continue to generate oxygen through photosynthesis. The increase in oxygen concentration was not a linear progression and occurred over a period of several hundred million years. Finally, while some bacteria can generate free oxygen through the breakdown of carbohydrates, this was not significant in terms of the oxygenation of Earth's atmosphere.

Which Statement About Oxygen and Ancient Earth Is True