I love paradoxes - embedded within them are sometimes interesting answers, or new ideas.

The paradox of chlorophyll is that it is most efficient in absorbing red light, whereas most of solar energy is in higher wavelengths. (This is why plants are green, of course - they absorb red and reflect the rest). Some scientists argue that chlorophyll simply happened to be an early-evolved photosynthetic compound that became "perfected" through evolution and reached a point that it was more efficient than any new competitor that might use the light "better".

I was thinking about this, and the apparent information that photosynthesis evolved early on, and added it to one of the atmospheric paradoxes of the Earth - that the Early Earth was NOT significantly colder than modern-day Earth, despite a lesser solar output.

And then I had another of my crazy intuitive ideas. What if the Early Earth had a blanket of smog or other atmospheric contaminants that rendered the atmosphere murky? This could have been dense enough to make noon-day sunshine like sunset - Red light.

The same dense blanket in the atmosphere would act as a strong greenhouse, keeping the Early Earth warm.

So chlorophyll was actually well-tuned to the sunshine *of the time in which it originated*.

After that, the "perfection" argument applies - once the atmosphere finally cleared (half or one billion years later?), it was too late for any new photosynthetic cycle to originate and be more efficient than chlorophyll.

So there we have it folks:- One answer that solves two paradoxes at once, and offers us clues to the composition of the atmosphere of the Early Earth...

(Any comments gratefully received)