The earth used to be purple

The ancient life on earth once covered a purple, not green as it is now. Ancient bacteria may have used a molecule other than chlorophyll to exploit sunlight, and this substance gives purple-colored organisms.

Chlorophyll, the main photosynthesis component of plants, absorbs mainly the red and blue waves from the sun and reflects the green wave, which is the reflected light that gives plants a green color. This disturbs some biologists because the green part of the spectrum is where the sun has the most energy.

"Why does chlorophyll reject the region with the most energy?" Said Shil DasSarma, a genetic geneticist at the University of Maryland, USA. Besides, evolution has made human eyes most sensitive to green light (which explains why these night-vision goggles often cover this green color). So why does the photosynthesis process not be adjusted like that?

DasSarma said that because chlorophyll appeared after another light-sensitive molecule called retinal existed on Earth. Retinal, present in the plum-colored membrane of a photosynthetic molecule called halobacteria, absorbs green light and reflects red and purple, bringing about a purplish purple color.

Primitive molecules that use retinal to harness solar energy may have dominated the ancient earth, thus making the first life areas on earth have outstanding purple colors.

As latecomers, chlorophyll-using molecules cannot compete directly with retinal-using organisms, but they survive by developing the ability to absorb light waves that retinal doesn't use. .

Researchers speculate that chlorophyll and retinal organisms already exist in parallel."You can imagine the situation where photosynthesis takes place right under the layer of the purple membrane," DasSarma said.

But then the scientists found that the balance tilted toward chlorophyll because it was more effective than retinal."Chlorophyll may not exploit the best of the spectrum, but it makes better use of the light it absorbs , " explains Sparks. Meanwhile retinal has a simpler structure than chlorophyll and works more easily in the original oxygen-deficient environment of the earth.

In addition, halobacteria, a living creature today using retinal, is not a bacterium. It belongs to the group of organisms called archaea, dating back to the earth's absence of atmosphere. All this shows that retinal was born earlier than chlorophyll, DasSarma concluded.

The group presented its purple earth hypothesis at the beginning of the year at the annual meeting of the American Astronomical Society and described the work in the latest American Scientist digital magazine.

MT