Earth's first plants were purple

Before Earth was green, it may have been purple - and the life we have today is the survivor that lost the first round.

The hypothesis, proposed by microbiologist Shiladitya DasSarma in 2007, starts with a pigment called retinal. Retinal is the same molecule your eye uses to detect light, and it absorbs the green wavelengths the Sun delivers most strongly. It's also simple, ancient, and far easier to evolve than chlorophyll. The earliest light-harvesting microbes, DasSarma argues, would have used it - and a microbe full of retinal looks purple.

For perhaps a billion years, purple haloarchaea may have dominated Earth's shallow seas and shorelines, soaking up the green light and reflecting back the red and blue. DasSarma suggests that because retinal microbes dominated the green spectrum, chlorophyll-based life evolved to use the remaining wavelengths - which is exactly the spectrum chlorophyll absorbs, and exactly why plants reflect green today.

If the story is right, the colour of every forest you've ever seen is a record of who came second.