Before 2002, the dogma surrounding rod and cone cells was that they were the only cells with photosensitive properties in the retina of the eye. It was also known that light entrainment and the circadian cycles are tuned by environmental influences. Scientists knew that exposure to different light cycles can reset the circadian clock, but did not know how this worked. Humans and mice that lacked rods and cones could still reset their circadian rhythms. They hypothesized that there must be another mechanism in the eye besides rod and cone photoreceptors to allow for this photosensitivity. Their question was: Could melanopsin be a photo pigment protein that allows retinal ganglion cells (RGC’s) to be light sensitive?
Comments
Overall this paragraph is
Overall this paragraph is well written. For scientific writing, however, I feel like you don't want to state their question in question form, but maybe right it as a hypothesis statement instead.
The first sentence implys
The first sentence implys that the dogma before 2002 was false (which it of course very may will be), however stating in the second sentence that "It was also known" seems somewhat awkward and may imply that the information presented here may also be false. I would therefore suggest that you instead state "At this time it was known that...."