Our beautiful "blue marble" with its accents of green and brown didn't always look the way it does now. Back in 2007, Professor Shiladitya DasSarma of the University of Maryland-Baltimore speculated that early life on earth may have been purple. And there is more and more evidence that this could be true.
The hypothesis is that Earth's earliest microbes were phototrophs, capturing photons from sunlight to produce energy for themselves. This isn't too surprising – the plants that dominate Earth today are also phototrophs. However, unlike modern plants, which utilize the pigment chlorophyll to capture light, these ancient microbes might have used a pigment called retinal. Chlorophyll absorbs red and blue light while reflecting green. Retinal does the opposite, meaning microbes making use of it would appear purple.
The San Francisco salt ponds pictured at the top of the article tease what Earth's oceans might have looked like billions of years ago. Back then, the planet was far hotter and bathed in copious ultraviolet light, with much higher concentrations of sulphur and methane. Modern retinal-using microbes call haloarchaea love these sorts of environments, and it could have been their descendants that dominated a purple planet.
So if that's the way it was, what changed along the way? Read how chlorophyll-producing plants took over in this speculative scenario at Real Clear Science. -via Damn Interesting
(Image credit: dro!d)