Early life may have been as 'purple as it is green today'

Early microbial life on Earth may have been purple, reports LiveScience. Somehow, they make the leap to a purple planet from there. The headline reads, "Early Earth Was Purple, Study Suggests." But they don't explain in the article how purple microbes would turn the whole planet purple. We have primarily green ones today, but our oceans aren't green. They're pretty much blue, right?

Anyway, the purple microbe theory comes from Shil DasSarma of the University of Maryland. And it's a way to explain why plants use the red and violet bands of the sun's light instead of the more energy-rich green band.

To understand this, let's start by comparing how two molecules, retinal and chlorophyll, convert the sun's light into energy. Retinal absorbs green light, which is the highest-energy band of the spectrum, but reflects red and violet light. Chlorophyll, of course absorbs blue and red light, and reflects green.

Retinal is the simpler of the two molecules, and "would have been easier to produce in the low-oxygen environment of early Earth." Also, retinal is present in halobacteria, a microbe that (despite its name) isn't really a bacteria, but an "archaea" that's been around since before the Earth had an oxygen-rich atmosphere.

DasSarma imagines a layer of purple microbes dominating in the Earth's early oceans, and a smaller population of green ones developing beneath it to pick up the scraps of the light spectrum.

Even though Chlorophyll relies on a lower-energy band of the spectrum, organisms using it probably dominated since it's more efficient at converting the sun's light into energy a plant can use.