It's hard to say exactly when oxygenic photosynthesis began since it may have been around on a limited scale for some time before it took off about 2.7 Gy ago, when it destroyed much of the life in a hitherto anaerobic world.
However, there have been several relatively brief periods in the...
Chlorophyll is green because it wasn't the first photosynthetic pigment. The first successful photosynthetic organisms were probably archaebacteria rather like the present-day Halobacterium halobium, which lives in salt lakes and can be thought of as a "living fossil".
It doesn't have...