World's 'oldest coloured molecules' are bright pink

The pink pigments are the fossilised molecules of ancient sea organisms

Scientists have discovered what they say are the world's oldest surviving biological colours, from ancient rocks beneath the Sahara desert.

The 1.1 billion-year-old pigments have a bright pink hue, but range from blood red to deep purple in their concentrated form.

The pigments are fossilised molecules of chlorophyll produced by sea organisms, Australian scientists said.

Researchers ground shale rocks into powder to extract the pigment.

"Imagine you could find a fossilised dinosaur skin that still has its original colour, green or blue... that is exactly the type of discovery that we've made," Associate Prof Jochen Brocks from the Australian National University (ANU) told the BBC.

"These are actual molecules, the oldest coloured molecules in the world.

"When held against the sunlight, they are actually a neon pink."

'Amazing that colour can survive'

ANU PhD student, Dr Nur Gueneli, discovered the pigments after running an organic solvent through the powdered rock. Mr Brocks said the extraction process was "similar to a coffee machine".

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"I heard her screaming in the lab when it came out, and she ran into my office," Asst Prof Brocks said.

"At first I thought it had been contaminated. It is just amazing that something with a biological colour can survive for such a long time."

Scientists extracted the molecules from ancient shale rock

A mining company had found the rocks in a marine shale deposit in the Taoudeni Basin in Mauritania, West Africa about 10 years ago, after drilling a hole several hundred metres deep, he said.

An analysis of the pigments found they had been produced by cyanobacteria in the seas at the time. Prof Brocks said this contributed to understanding on the evolution of life forms on Earth.

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"Tiny cyanobacteria dominated the base of the food chain in the oceans a billion years ago, which helps to explain why animals did not exist at the time," he said.

"Life only became bigger about 600 million years ago because before that there was no sufficient food source."

The research, which also involved scientists in the US and Japan, has been published in journal Proceedings of the National Academy of Science of the United States of America.