The Verse - Volume 36
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Purple Particulars – Imagine a Purple Earth

The earliest life on Earth might have been just as purple as it is green today, a scientist claims.

Ancient microbes might have used retinal, a molecule other than chlorophyll, to harness the Sun's rays, one that gave the organisms a violet hue.

Chlorophyll, the main photosynthetic pigment of plants, absorbs mainly blue and red wavelengths from the Sun and reflects green ones, and it is this reflected light that gives plants their leafy green color. This fact puzzles some biologists because the sun transmits most of its energy in the green part of the visible spectrum.

"Why would chlorophyll have this dip in the area that has the most energy?" said Shil DasSarma, a microbial geneticist at the University of Maryland. DasSarma thinks it is because chlorophyll appeared after another light-sensitive molecule called retinal was already present on early Earth. Retinal, today found in the plum-colored membrane of a photosynthetic microbe called halobacteria, absorbs green light and reflects back red and violet light, the combination of which appears purple.

Primitive microbes that used retinal to harness the sun's energy might have dominated early Earth, DasSarma said, thus tinting some of the first biological hotspots on the planet a distinctive purple color.