The color of life in the universe

Part of the reason plants are green is that at the beginning of their history, they probably had to compete with other organisms.

These were able to make use of sunlight thanks to a pigment called retinol.

Organisms equipped with retinol were the first to carry out photosynthesis, and since the molecule absorbs green light (which is also the most abundant light that reaches Earth) the most efficiently, they reflected the blue and red components of the solar spectrum and thus had a violet color.

Later, with the development of chlorophyll, plants began to compete with these purple life forms, using the frequencies that were not absorbed by the latter and reflecting green instead.

Retinol-based photosynthesis is much less efficient than chlorophyll-based photosynthesis, more rudimentary, but for this very reason, also much easier to achieve. It is still used in numerous species of bacteria and archaebacteria, and retinol is also found in the vision systems of more complex animals.

The fact that these pigments are extremely widespread in all life on Earth indicates that their evolution must have been very easy and early.

Since retinol is a simpler molecule than chlorophyll and one that already allows for rudimentary photosynthesis, it could also be common in life on other planets. Perhaps even a nearly mandatory step in the evolution of life in general.

If so, the typical and most common color of flora on planets populated by life forms would be purple.

A color that could therefore be the distinctive bio-signature of life in the universe.