Did the first algae create the oxygen in the atmosphere?

Yes, the first algae, particularly cyanobacteria, played a crucial role in creating oxygen in the Earth's atmosphere through the process of photosynthesis. Around 2.4 billion years ago, these microorganisms began to produce oxygen as a byproduct of converting sunlight, carbon dioxide, and water into energy. This event, known as the Great Oxidation Event, significantly increased atmospheric oxygen levels and transformed Earth's environment, making it more conducive to the evolution of aerobic life forms.