Imagine that scientists have discovered a new planet that is apparently devoid of life but has ice caps located at the poles. these ice caps reveal that the planet's atmospheric o2 levels sharply increased about 1,000,000 years ago but then quickly dropped 50,000 years ago. what could account for these changes in atmospheric o2 levels?

Photosynthetic organisms was the reason of these atmospheric changes.

Explanation:

The plant which is discovered by the scientists that is apparently devoid of life but has ice caps located at the poles which reveals that planet's atmospheric O₂ levels sharply increased about 1,000,000 years ago was due to evolution of photosynthetic organisms like cyanobacteria etc which went extinct and then O₂ levels dropped quickly 50,000 years ago. So photosynthetic organisms was the reason of these atmospheric changes.