Hypoliths, communities of blue-green bacteria found underneath quartz rocks, could hold the secret to life on other planets.

For life, there must be an organism at the base of the food chain, a primary producer.

Desert ecosystems shows the outer limits of what life can withstand.

“If you’re going to find life on Mars, it is not going to be a zebra,” says Wits University’s Professor Duncan Mitchell.

And scientists all over the world are hunting for present or past life on Mars, and on other planets. Many are looking to extreme environments, such as Namibia’s Namib desert, to see what what sort of pressures life can handle.

Hypoliths, communities of blue-green bacteria found underneath quartz rocks, could hold the secret to life on other planets. Known as extremophiles, these bacteria have created a cosy niche for themselves: the quartz rock exposes them to light, while protecting them from the desert’s scorching temperatures and the sun’s ferocious solar radiation.

Scientists want to know “what type of life would survive in harsh environments”, says Mitchell. “That means you don’t waste your time on Mars looking for things that are completely out of line with what is possible.”

Chris McKay, a senior scientist at Nasa’s Ames Exploration Centre in California, is interested in deserts for this reason. “For life, there must be an organism at the base of the food chain, a primary producer.”

These blue green smudges on the undersides of rocks in hyper-arid deserts are one of those base organisms. Don Cowan, head of the Centre for Microbial Ecology and Genomics at the University of Pretoria, studies these hypoliths in both the Namib desert and the dry plains of Antarctica. He calls them the “rainforests of the deserts”.

“The fact that [in the Namib] the soil is dry for 51 weeks of the year and temperatures at the surface of up to 60 to 65 degrees Centigrade doesn’t prevent microbial life from occurring here, and I’d like to know what’s there, what it’s doing, how it survives, and how it has adapted to survive,” he says.

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