While on Earth, this theoretical retinal-based life is believed to have been out-competed and suffocated by oxygen-producing chloroplasts, and this process might not happen or have happened yet on other worlds. Data may one day come back that is consistent with a purple world, a color which may be a sign of alien life flourishing given its few non-biological sources (via CNN). The simpler composition of retinal pigment may even make it a universal building block for extraterrestrial life, rendering Earth a galactic oddity. 

With this in mind, it is important to explore why such retinal supremacy may have never happened. The Purple Earth theory came about in response to evidence that showed that chloroplasts were not absorbing the amount of light they should have when they first appeared in the fossil record. Per the hypothesis, this is because retinal life was dominant at the time and took in most ultraviolet rays. However, this could just as easily be the result of chloroplasts responding to excess sunlight or some other environmental factor (via Live Science). Nevertheless, if the theory is verified, Earth will have yet another strange chapter of its history exposed.