To order the events chronologically based on the history of Earth's atmosphere and the evolution of life, the correct sequence is:
- Single-celled organisms increase atmospheric methane concentrations.
- Photosynthesizing bacteria release oxygen into the sea.
- Oxygen concentrations increase in the atmosphere.
- Many new animal species evolve.
Thus, the option that correctly orders the events is:
"Single-celled organisms increase atmospheric methane concentrations. Photosynthesizing bacteria release oxygen into the sea. Oxygen concentrations increase in the atmosphere. Many new animal species evolve."