TRAVEL through the arid south-west of the US, or across the dry fringes of the Gobi desert of western China, or over the mountain deserts of the Argentine Andes, and you could see a strange sight. The apparently bare rocks of these parched places are often coated with a mysterious, brightly coloured film. It is as if someone, or something, has painted the desert.
Chip away at this coating, and you will see that is exactly what has happened. The rocks are covered with a wafer-thin "varnish". It is created by colonies of bacteria that live on the surface of the rocks and extract energy by oxidising minute quantities of metals such as manganese, blown in on airborne dust and in the debris falling in occasional rain showers.
This secret landscape, often as pervasive as grass on pasture, is beginning to tell a remarkable story. It is helping to unlock ...
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