The Purple Hills of Earth?

"Early Earth Was Purple, Study Suggests"
LiveScience (April 10, 2007)

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

"Ancient microbes might have used 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 color. This fact puzzles some biologists because the sun transmits most of its energy in the green part of the visible spectrum...."

The key word here is "might." The idea is that early photosynthetic organisms might have used retinal, instead of chlorophyll, to get energy from sunlight. There are microorganisms around today that use retinal this way: halobacteria. They're not actually quite bacteria: halobacteria are part of a very ancient group of organisms called archaea.

There's a rather mind-numbingly technical discussion of halobacteria at "MICR 425: PHYSIOLOGY & BIOCHEMISTRY of MICROORGANISMS - HALOBACTERIA" (Southern Illinois University, Carbondale, College of Science (August 3, 1999)).

I can't see how this will help you find a better prices at the grocery, or help me attract more hummingbirds to the feeder.

On the other hand, it's a fascinating bit of informed speculation about what Earth was like a few billion years back. Also, when looking for life around other stars, it's likely that we shouldn't assume that plants are always green. Or, for that matter, that photosynthetic creatures are always plants.

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Related posts, at

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"