On Tuesday, a team of scientists from Australian National University announced that it had discovered the oldest colors ever seen in the geological record. The pigments, which ranged from red to purple and look pink when diluted, were discovered below the Sahara desert in north Africa.
A small caveat is needed here. Obviously, rocks existed on Earth more than 1.1 billion years ago and rocks have color. When the scientists refer to the oldest colors on Earth, they are referring to biological pigments—that is, the oldest color produced by living things.
As detailed in a paper published in the Proceedings of the National Academy of Sciences, the pigments were derived from molecular fossils of chlorophyll, which was produced by ancient organisms called cyanobacteria. Chlorophyll is the green pigment found in cyanobacteria and every living plant that absorbs sunlight and uses this energy to fuel photosynthesis. The pigments are derived from fossilized porphyrins, a type of organic compound that forms an atomic ring around a magnesium ion to form a chlorophyll molecule.
The researchers discovered the chlorophyll by crushing billion-year-old rocks and extracting the molecular porphyrin fossils from the dust. The discovery in itself is quite remarkable, given that ancient food sources such as bacteria and algae don’t leave easily identifiable fossilized remains. So instead of looking for the bacteria and algae itself, the researchers sought out its fossilized biomarkers, such as porphyrins indicating the production of chlorophyll.
The finding is a major step toward answering the question about why large, active organisms didn’t inhabit Earth’s oceans around a billion years ago. One hypothesis suggested the reason was a lack of large food particles, such as planktonic algae. Although this type of algae is still pretty small in the general scheme of things, it is still roughly a thousand times larger than the cyanobacteria that produced the chlorophyll discovered by the Australian researchers.
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The new research provides strong evidence for this theory by demonstrating that Earth’s oceans were dominated by cyanobacteria, which wouldn’t have provided enough energy to lead to the emergence of large, complex life. It was only when the dominance of cyanobacteria in Earth’s ocean was superseded by more energy-dense food sources, such as planktonic algae, that conditions were favorable for more complex life.
“The cyanobacterial oceans started to vanish about 650 million years ago,” said Jochen Brocks, an associate professor of earth sciences at Australian National University. “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.”