The correct answer is D.
From the scientific research conducted so far, we know that in the early Earth's history the atmosphere lacked oxygen and was mostly filled with other gases like methane. The increase in oxygen levels happened when the plants started producing oxygen as a byproduct of the process of photosynthesis.
The research so far also shows that the RNA was present before the DNA and that the microspheres might have been essential to the development of life on Earth.
