Oxygen was first introduced into Earth's atmosphere by:

Question

Quizplus · Accepted Answer

Cyanobacteria are believed to be the first organisms to produce oxygen through photosynthesis, which would have introduced it into the Earth's atmosphere over 2 billion years ago. While volcanic activity also played a role in the composition of the early atmosphere, it was not the primary source of oxygen. Dinosaurs and trees evolved much later in Earth's history and did not significantly impact the introduction of oxygen to the atmosphere.

Oxygen Was First Introduced into Earth's Atmosphere By