Surprisingly, the world’s oldest color in the geological record is bright pink, according to new research by an international team of experts and collected in the journal Proceedings of the National Academy of Sciences.
Scientists extracted the pigment from fossil bacteria preserved in rocks under the Sahara desert in Mauritania, West Africa. Within these bacteria they discovered that chlorophyll, a pigment used today by plants for photosynthesis, dates back to about 1.1 billion years ago. That’s roughly 600 million years older than similar chlorophyll fossils found previously.
Their findings suggest that cyanobacteria, bacteria that survive in sunlight, appeared long before algae, dating back to about 650 million years ago. And bacteria likely dominated Earth’s ancient oceans for hundreds of millions of years.
Chlorophyll is what gives modern plants their green color, we already know that; however, the fossilized chlorophyll in the cyanobacterial samples was dark red and deep purple in its concentrated form , the scientists reported.
When they pulverized the fossils to analyze the bacteria molecules, they distilled the colors and the result was: a bright pink. This remnant color suggests that ancient organisms that absorbed sunlight cast a pinkish tint into a vanished ocean, says Nur Gueneli, of the Research School of Earth Sciences at the Australian National University (ANU) and leader of the work.
Such an old chlorophyll is only preserved under exceptional circumstances. First, dead organic matter (a cyanobacterial bloom, for example) quickly sinks to the seafloor. Once there, it must be insulated from any exposure to oxygen, which stimulates decomposition, and then the rock containing the material must remain in one piece for 1 billion years, says Jochen Brocks, a co-author of the study.
When scientists saw the colors produced by organisms that lived more than 1 billion years ago, their reaction was this: “It’s a big surprise,” said Brocks. Even algae, one of the oldest forms of life, were absent or in short supply at the time these bacteria swallowed the chlorophyll.
It took a few hundred million years for the algae to begin to multiply, eventually forming the basis of a food web that would eventually fuel the evolution of larger animals. But, until the emergence of algae and more complex organisms, the planet belonged to bacteria.
Thus, the cyanobacterial oceans began to disappear about 650 million years ago , at which time algae began to spread around the planet and where, later, large animals, including humans, would thrive.
Reference: N. Gueneli el al., “1.1-billion-year-old byphyrins establish a marine ecosystem dominated by bacterial primary producers,” PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1803866115
