Which of the following organisms first introduced oxygen into Earth's atmosphere?

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Cyanobacteria, also known as blue-green algae, were the first organisms to introduce oxygen into Earth's atmosphere through photosynthesis. This process began around 2.4 billion years ago and eventually led to the development of Earth's oxygen-rich atmosphere. Green algae and plants evolved later and also contribute to the oxygen content in the atmosphere, but cyanobacteria were the pioneers in this process. Early protozoans are not known to have played a significant role in oxygen production.

Which of the Following Organisms First Introduced Oxygen into Earth's