The Mono Lake Research Area: site of a second type of life?
The idea of searching for a 'shadow biosphere' is that if we can identify life on Earth that is unrelated to other life on Earth, then this will prove that life started here twice, independently. That simple finding would show that it is likely that life could start on other planets too.
This is explored in an upcoming Bang Goes the Theory special, The Search For Life, where we include a visit to Felisa Wolfe-Simon in the lab while she was culturing the arsenic-loving bacteria.
What has been found in Mono Lake is bacteria that can use arsenic in place of phosphorous to build nucleic acid (in links between the sugar groups in their DNA).
Felisa Wolfe-Simon performed experiments in which she gradually increased the arsenic concentration in lab cultures of arsenic-tolerant bacteria from Mono Lake until all that was growing was bacteria that used arsenic in place of phosphorous.
This certainly makes these organisms a very remarkable variety of 'extremophile'. I think the jury is still out as to whether they are descended from life that began separately to other known life on Earth.
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