When the earth was purple

Have you ever wondered why the vast majority of plants and trees have green

leaves and not some other color?

It’s always been a bit of a mystery why plants absorb red and blue light, but

reflect green, allow us to see the leaves as green. It seems inefficient of

nature when the sun emits the peak energy of its visible spectrum in the

yellow-green areas. A new theory offers one possible answer: that the first

chlorophyll-utilizing microbes evolved to

exploit the red-and-blue light that older green-absorbing microbes didn’t use,

eventually out-competing them through

greater efficiency and the rise of oxygen.

If that were the case, plant life long ago may have had purple leaves to

catch both the red and blue portions of the spectrum. For those whom don’t know

this, RED + BLUE =

MAGENTA (purple)

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John Dittes
April 26, 2007 4:59 pm

Hello there Anthony,
Another interesting link. Curious to see what comes of the idea after peer review.
By the way, I learned a different idea regarding the origin of a “green” chlorophyll pigment as the principal light harvesting molecule in plants. I’m surprised that the researcher cited nor the article’s author doesn’t mention it. It’s commonly held and seems to make more sense than competative exclusion between microbes in the vast expanse, varied depths and myriad niches of the world’s oceans.
According to what I was taught, photosynthetic life originated in the ocean at a time when there was no free oxygen, and therefore no ozone in the atmosphere.
As a consequence, any marine microbes washed ashore or circulated into the upper few feet of the ocean surface were quickly destroyed by UV radiation (now filtered by ozone). At that time, there was not yet any terrestrial life.
Also and importantly, the wavelengths first lost (attenuated) with increasing water depth happen to be green.
Green, being the least available wavelength at depths where photosynthetic organisms most likely evolved was a useless color, simply because it is not there in abundance below the “UV-Death Zone” for energy capturing/conversion, unlike red and blue wavelengths.
Over many millions of years, as oceanic photosynthetic (green) organisms saturated the ocean, oxygen diffused into the atmosphere where it accumulated and interacted with UV radiation to form the crtically protective ozone layer.
Only as the ozone layer developed to become a protective barrier, evolving aquatic life forms were able to live closer to the surface, and then spread and diversify onto land.
By that time though, the chlorophyll-based photosynthetic light-harvesting apparatus was so efficiently evolved and well established, nothing could evolve in time better to “beat it”. There are lots of non-green accessory pigments since evolved to complement and work with the main green molecule, but none really replace it.
Alternatively of course, green just might be GOD’s favorite color…simple as that!
Afterall, purple (magenta)is avoided as a paint color in prisons, psychiatric wards and schools because of its potentially negative psychological influences. Purple just wouldn’t have worked out!
Thanks for the link,
John D.

April 26, 2007 7:49 pm

Thanks for the refresher course John.
But with this latest revelation, it goes to show you that the natural world is purplexing.

Mike McMillan
September 8, 2008 10:29 pm

If that were the case, plant life long ago may have had purple leaves to
catch both the red and blue portions of the spectrum. For those whom don’t know this, RED + BLUE = MAGENTA (purple)

Yes for crayolas, no for plants. Magenta leaves would absorb the green, yellow, and cyan (aqua) shade, reflecting the red and blue wavelengths you saw as purple. Red, green, and blue are the additive colors in a computer monitor that make white light, while cyan, magenta, and yellow are the subtractive inks that printers put on paper to absorb unwanted colors from white light. Yellow and cyan combined will absorb everything but green.
Purple pond scum. Hardly a suitable ancestor.

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