Surprisingly, the world’s oldest color in the geological record is bright pink, according to new research conducted by an international team of experts and compiled in Proceedings of the National Academy of Sciences.
The scientists extracted the pigment from the fossil bacteria preserved in rocks under the Sahara desert in Mauritania, in West Africa. Within these bacteria, they discovered that chlorophyll, a pigment used today by plants for photosynthesis, dates from about 1.1 billion years ago. That is about 600 million years older than the similar chlorophyll fossils found earlier.
Their findings suggest that cyanobacteria, bacteria that survive with sunlight, appeared much earlier than algae, which date back to about 650 million years ago. And bacteria probably dominated the ancient oceans of Earth 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 dark purple in its concentrated form, the scientists reported.
When they pulverized the fossils to analyze the molecules of bacteria, they distilled the colors and the result was: a bright pink. This remnant color suggests that the ancient organisms that absorbed sunlight cast a pink tint into a vanished ocean, says Nur Gueneli, of the Earth Sciences Research School of the Australian National University (ANU) and leader of the work.
An old chlorophyll is only preserved under exceptional circumstances. First, the dead organic matter (a flowering of cyanobacteria, for example) sinks rapidly into the seabed. Once there, it must be isolated from any oxygen exposure, which stimulates decomposition, and then the rock containing the material must remain in one piece for 1 billion years, says Jochen Brocks, co-author of the study.
When scientists saw the colors produced by organisms that lived more than 1,000 million 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 scarce at the time these bacteria swallowed chlorophyll.
A few hundred million years passed until the seaweed began to multiply, eventually forming the basis of a trophic network that would eventually feed the evolution of larger animals. But, until the rise 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 the algae began to spread throughout the planet and where, later, large animals, including humans, would thrive.