And that pigment was a fetching shade of pink.
Not only does the find provide tangible evidence of ancient photosynthesis, analysis of the compounds indicates they were left behind by bacteria, which helps explain why animals took so long to show up in the evolutionary record.
An international team of researchers found the preserved signature for chlorophyll inside 1.1 billion-year-old marine black shales dug up out of the Taoudeni Basin in Mauritania, West Africa.
Crushed up and diluted, the raw material is a pinkish hue. But don’t let that fool you: the microscopic life that left it behind was probably far more vibrant.
In the 1960s there were reports of similar fossils uncovered from rocks up to several billion years old, but these days they’ve generally been dismissed as unreliable.
While chlorophyll itself is green, these building blocks tend to come in strong shades of reds and purples – hence why this latest fossilised pigment comes in pink.
Considering oxygen levels started to rise around 3.4 billion years ago, that earlier find still left us with a big gap in fossil evidence of sunlight-harvesting pigments.
But the latest discovery is more than just confirmation of ancient pigments (it’s not like we thought the world was black-and-white before this). The very nature of the molecules tells us something important about the organisms that made them.
A closer look at the specific isotope of nitrogen making up the compounds reveals the organisms weren’t at all plant-like in nature.
“The precise analysis of the ancient pigments confirmed that tiny cyanobacteria dominated the base of the food chain in the oceans a billion years ago,” says the study’s lead author Nur Gueneli from The Australian National University (ANU).
But the fact simple microbes seemed to rule the base of the food pyramid so late in the Precambrian world helps sway arguments that suggest bigger, more complex consumers weren’t yet evolving simply because the food supply wasn’t there.
That means nothing was swimming around, chomping down on morsels of sunbaking cyanobacteria. It’s likely their puny size just didn’t offer enough incentive; it took the evolution of a richer food source for animals to really get a leg up.
“Algae, although still microscopic, are a thousand times larger in volume than cyanobacteria, and are a much richer food source,” says geochemist Jochen Brocks from the ANU.
“The cyanobacterial oceans started to vanish about 650 million years ago, when algae began to rapidly spread to provide the burst of energy needed for the evolution of complex ecosystems, where large animals, including humans, could thrive on Earth.”
Exactly what kicked off this whole changing of the guard is still a matter of debate, but other research from ANU suggests it all came down to a warm spell after a big freeze.
Earth had been in the grip of an epic winter that beat any Game of Thrones scenario, one that released a torrent of ice-trapped nutrients when it started to thaw.
The change benefited an underdog called Archaeplastida, whose odd partnership represented the first eukaryotic organisms.
The whole affair kicked off a takeover that quite literally changed the world, one that not only made it more colourful in the end, but a lot more exciting.
This research was published in PNAS.