Are we sharing our planet with unusual and invisible lifeforms?
In the Atacama desert in Chile, the Mojave desert in California and many other arid locations, a strange ‘sheen’ made up of manganese, arsenic and silica can be found on rock surfaces. Despite intensive research, it is not yet known how this desert varnish forms but one researcher has presented a particularly interesting theory.
Carol Cleland, Professor of Astrobiology at Colorado University, believes that the sheen could be the manifestation of an alternative, invisible biological world, which she calls the shadow biosphere . "The idea is straightforward," she says. "On Earth we may be co-inhabiting with microbial lifeforms that have a completely different biochemistry from the one shared by life as we currently know it."
The concept of a shadow biosphere was first presented by Cleland and her colleague Shelley Copley in the International Journal of Astrobiology in 2006, and is now supported by many other scientists, including astrobiologists Chris McKay, who is based at Nasa's Ames Research Centre, California, and Paul Davies.
Cleland explains how it is possible to have a lifeform that has remained undetectable to modern science: "All the micro-organisms we have detected on Earth to date have had a biology like our own: proteins made up of a maximum of 20 amino acids and a DNA genetic code made out of only four chemical bases: adenine, cytosine, guanine and thymine, yet there are up to 100 amino acids in nature and at least a dozen bases. These could easily have combined in the remote past to create lifeforms with a very different biochemistry to our own. More to the point, some may still exist in corners of the planet."