Answer:
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 Oâ‚‚ levels sharply increased about 1,000,000 years ago was due to evolution of photosynthetic organisms like cyanobacteria etc which went extinct and then Oâ‚‚ levels dropped quickly 50,000 years ago. So photosynthetic organisms was the reason of these atmospheric changes.
