Imagine Earth not as the blue and green orb we know today. Imagine it as a psychedelic purple planet. According to microbial geneticist Shil DasSarma from the University of Maryland, ancient purple microbes dominated early Earth.

Today's plants are green because of chlorophyll - the pigment that makes photosynthesis possible. Green leaves absorb the reds and blues in the electromagnetic spectrum (or wavelengths of light) and reflect the greens. The fact is that the sun transmits most of its energy on the greens - so why did today's plants evolve not using the precious green light?

According to DasSarma, the explanation might be simple. There might have been another light-sensitive molecule that takes the green and reflects the reds and blues which causes it to emit a purple color. This ancient light-sensitive molecule was dubbed "retinal" and can be found today in another photosynthetic microbe called halobacteria.

DasSarma speculates that the retinal microbes dominated early Earth (imagine a massive clump of them making a purple spot on the Earth). The chlorophyll using microbes came later and evolved to harness the reds and blues that the retinals did not use since they couldn't complete with the then big boys. So how did chlorophyll become the dominant color? It may have been that the greens were simply more efficient than the purple retinals. According to William Sparks, an astronomer for the Space Telescope Science Institute in Maryland, "Chlorophyll may not sample the peak of the solar spectrum, but it makes better use of the light that it does absorb." DasSarma's theory is still based on speculation but the information fits with what scientists already know. The evidence that shows that retinal developed earlier that chlorophyll:

• Retinal has a simpler molecular structure than chlorophyll, which made it easier to produce in oxygen deprived early Earth
• Retinal production followed a process that resembles that of fatty acid and scientists think that the acid is essential in the development of cells.
• The halobacteria (misnomer since it's not a bacteria but a mibrobe) comes from an ancient group called archaea which dates back to a prehistoric Earth sans the oxygen atmosphere.

I think when most people think about remote sensing, they're focused on chlorophyll-based life, it may be that is the more prominent one, but if you happen to see a planet that is at this early stage of evolution, and you’re looking for chlorophyll, you might miss it because you're looking at the wrong wavelength.