Canberra scientists have crushed billion-year-old rocks to discover the world's oldest biological colours, bright pink pigments that shed light on the reason humans and animals did not exist until relatively late in Earth's history.
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Scientists from the Australian National University extracted the pigments from 1.1 billion-year-old rocks found deep beneath the Sahara Desert.
Australian National University senior lead researcher Dr Jochen Brocks said a petroleum company found the rocks in a marine shale desposit about 10 years ago, after drilling a hole several hundred metres deep while looking for oil in the Taoudeni Basin in Mauritania, West Africa.
Dr Brocks said researchers had expected to find a crude, black colour when they started examining the rocks in Canberra, and were shocked to discover bright pink pigments.
"There was this scream in the lab and [Dr Nur Gueneli] came running into my office," Dr Brocks said.
"She said, 'Look at this, Jochen', and she had this bright pink stuff.
"It's just spectacular that these pigments could survive for that long."
The pigments range from blood red to deep purple in their concentrated form, but are bright pink when diluted.
Dr Gueneli, who made the discovery as part of her PhD studies, said the pigments were more than 500 million years older than previous discoveries.
She said the pigments were molecular fossils of chlorophyll produced by "ancient photosynthetic organisms inhabiting an ancient ocean that had long since vanished".
Dr Brocks said an analysis of the pigments showed they were being produced exclusively by tiny cyanobacteria in the oceans of 1.1 billion years ago.
He said this explained why Earth, which was about 4.6 billion years old, had only been home to larger, animal-like creatures for about the last 600 million years.
"Algae, although still microscopic, are 1000 times larger in volume than cyanobacteria, and are a much richer food source," Dr Brocks said.
"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."
The new research, led by the Australian National University and supported by Geoscience Australia and researchers in the US and Japan, has been published in the journal Proceedings of the National Academy of Sciences of the United States of America.
