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A purple Earth? Life began as a shade of lavender — and alien life may, too, study says

Purple may have been the first color of life on Earth because early organisms absorbed the sun’s energy using the molecule retinal instead of Chlorophyll, important for photosynthesis and a giving greenish hue.
Purple may have been the first color of life on Earth because early organisms absorbed the sun’s energy using the molecule retinal instead of Chlorophyll, important for photosynthesis and a giving greenish hue. NASA

Imagine what Earth would look like if all of its lush greenery turned, well, purple.

That otherworldly fantasy could have actually been a reality during the dawn of life on our planet, a new study says, as the first organisms on Earth might have developed a way to get energy by absorbing energy from sunlight using the molecule retinal.

That discovery means Earth might have sported a shade of lavender in the distant past — and it could help as we look for alien life on other planets throughout the galaxy, according to the study published in the International Journal of Astrobiology.

Currently, plants on Earth use the green-hued molecule chlorophyll to help convert carbon dioxide into oxygen and fuel life on Earth, as noted by the study. But researchers suggest that life might have started out using purple-colored retinal to get needed energy.

A fireball flew across the sky over Phoenix, Arizona, at around 8:30 pm on Tuesday, November 14. A security camera stationed at the Phoenix City Hall captured the sight, as seen in this video.

Life using retinal molecules absorb green and yellow light, the study says, then emit a mix of blue and red light that comes out purple.

And they aren’t a thing of the past, University of California astrobiologist Dr Edward Schwieterman told Astrobiology Magazine.

“Retinal-based phototrophic metabolisms are still prevalent throughout the world, especially in the oceans, and represent one of the most important bioenergetic processes on Earth,” the study’s co-author said, according to the newspaper.

Around 2.4 billion years ago, the Earth — at that point with an atmosphere high in methane and carbon dioxide — experienced a rapid increase in the amount of oxygen. The study’s authors believe that plants used both retinal and chlorophyll at that time to absorb energy, but an organism named cyanobacteria used photosynthesis at that time to push more oxygen back into the atmosphere.

The study estimates that both chlorophyll and retinal co-existed to absorb energy from the sun at different wavelengths, even though the retinal came first.

Organisms use retinal molecules to absorb the sun’s light peaking at wavelengths of 568 nm, which falls into the range that chlorophyll doesn’t, the study says. As noted by The Great Lakes Ledger, that led scientists to wonder if retinal was the “something else” that already capitalized absorbing the sun’s energy at that specific wavelength before the uptick in oxygen around 2.4 billion years ago.

“This is exactly what got us thinking that the two pigments – retinal and chlorophyll – may have co-evolved,” said University of Maryland School of Medicine microbiologist Shiladitya DasSarma, according to Astrobiology Magazine.

So what does this mean for the search for aliens?

Basically, if it happened here on Earth, it could happen elsewhere. So, scientists behind the study suggest we should broaden the scope of what types of organisms we look for on exoplanets when trying to figure out if we are alone in the universe.

Specifically, we should start looking for a “green edge,” the study says.

Scientists are currently looking for a “red edge” on distant planets with chance for life since organisms using chlorophyll reflect infrared red light, just as they do here on Earth. Since it’s the main type of life we know, it’s a method used by those hunting for aliens.

But if a planet had life primarily operating with retinal molecules, the study says, you should expect to see a “green edge.” And that may be what we find in the future in space, DasSarma said, as his study found retinal is both “simple” and “common,” LiveScience reported.

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