Fossils can tell us quite a bit about plants and animals that lived millions of years ago, including their size, shape and even a bit about their love life. But one thing they can’t do is reveal what color the creatures were. Was T. rex shades of turquoise and green, or muddy brown like it’s depicted in most art? It’s hard to say since the organic pigments that produce color typically degrade over time. But it turns out some bits of color can last, and Luke Henriques-Gomes at The Guardian reports that scientists have discovered the oldest organic color so far, a bit of bright pink that has survived in 1.1-billion-year-old rocks.
The organic pigments come from oil shale deposits drilled by an energy exploration company in the Taoudeni Basin in Mauritania, West Africa, about ten years ago. According to a press release, researchers pulverized some of the rock to try and extract molecules from any ancient organisms trapped inside. The presence of the surviving pigment, however, was a complete surprise. Grad student Nur Gueneli at Australian National University realized she found something special after mixing the powdered material with an organic solvent. According to Blake Foden at The Sydney Morning Herald, the team expected the mixture to turn black. Instead the solvent turned pink. “I remember I heard this screaming in the lab,” Jochen Brocks, senior author on the paper in Proceedings of the National Academy of Sciences tells Henriques-Gomes. “[Gueneli] came running into my office and said, ‘look at this,’ and she had this bright pink stuff…It turned out to be real pigment, 1.1 billion years old.”
The BBC reports that the pigment comes from the chlorophyll of fossilized cyanobacteria, also known as blue-green algae, whose pigment molecules have survived eons in the ground. When diluted, the molecules look pink when held against sunlight, but in their concentrated form they appear red and purple. For researchers looking at the earliest traces of life on Earth, finding the organic pigment, which is 600 million years older than the oldest previous example, is startling. “Imagine you could find a fossilized dinosaur skin that still has its original color, green or blue... that is exactly the type of discovery that we’ve made.”
The discovery also highlights one of the big mysteries in the evolution of life on Earth. Despite being 4.6 billion years old, an explosion of complex life on Earth didn’t take place until about 650 million years ago. Some researchers have found evidence that oxygen concentrations on Earth, most created by cyanobacteria, just weren’t high enough to support life until that point, which would explain why life stayed single-cell for so long. Other recent studies, however, indicate that there was enough oxygen around for 1 billion years before complex life emerged. If that’s the case, then something else was the limiting factor. Brocks believes oceans dominated by cyanobacteria may be the culprit. The sample from the Sahara may be evidence that the cyanobacteria were the dominant lifeform on Earth over a billion years ago and caused an evolutionary bottleneck.
“Algae, although still microscopic, are 1000 times larger in volume than cyanobacteria, and are a much richer food source," Brocks tells Foden. “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.”
Some of those larger animals were, of course, the dinosaurs. And we’re starting to get a few clues about their color as well, at least the ones with feathers. By comparing melanosomes, microscopic structures that give modern bird feathers color, with the melanosomes found in the few fossilized dino feathers we have, researchers are now able to guess what color their plumage was. And who knows—maybe they'll find that some of them were bright pink as well.