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ANU biogeochemistry lab manager Janet Hope holding a vial of pink coloured porphyrins representing the oldest intact pigments in the world. Photo: ANU

World’s oldest colours paint picture of early life

Ask a child to colour in a stegosaurus and you might get a red one, a green one, or perhaps grey and blue. Ask a scientist and you might get the same variation.

That’s because colour is often lost to history and there’s only so much science can do to get it back. But Australian and international researchers are currently making headlines for doing just that.

They’ve discovered the world’s oldest colours in the geological record.

Some might say ‘but there’s colour in everything’. But Australian National University (ANU) Associate Professor Jochen Brocks said the research team is talking about colour in a different way. “I like the following analogy: just imagine you start digging out dinosaur bones in your backyard and you find fossilised bones of a T-Rex. Now, that will have a colour. It will be grey or brown. Something like that. It’s the colour of the rock and that always existed. That colour will not tell you anything about the actual colour of that bone when it was fresh. It also doesn’t tell you anything about the colour of the T-Rex.

“But now imagine you could find fossilised dinosaur skin that still preserves its original colour. Of course no one has ever found something like that, but that’s exactly the type of discovery that we made.

“We found this type of biological, preserved colour, only that our colour is another 15 times older than the oldest T-Rex. It’s a biological, molecular colour.”

The one in question was bright pink when diluted – as the team found few molecules – but if it was in a much more concentrated form, it would range from blood red to very deep purple.

The pigments were found in rocks deep beneath Africa’s Sahara Desert and have been dated back 1.1 billion years. The team crushed black shales of the Taoudeni Basin in Mauritania, West Africa then extracted from them molecules of ancient organisms.

ANU researcher Dr Nur Gueneli said the pigments are the molecular fossils of chlorophyll that were produced by ancient photosynthetic organisms inhabiting an ocean that has long since vanished.

Still, the colour of those organisms was not bright pink, or blood red or even deep purple. Brocks said the organism was a blue-green. It likely obtained the warmer colour – probably a few thousand years after the organism died – because the unstable magnesium atom at the centre of the molecule was replaced by a nickel (bright red) or vanadium atom (purple).

It’s not just the beauty of the pink pigment that has the research team excited – Brocks said it also helps to answer one of science’s longest-held questions: why did large, complex, multi-cellular creatures like our ancestors appear deceptively late in Earth’s history?

“This pink pigment tells us that the bottom of the food chain was made up of bacteria… but that larger, more nutritious single-celled algae, which are in volume about a 1,000 times bigger, did not exist. One hypothesis is because these big chunks of nutritious food didn’t exist, animal-like ecosystems could not evolve.

“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.”

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