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Aliens in Our Midst

As we seek out organic compounds and water on the surface of Mars, ponder the potential for hidden oceans on Europa, and discover new Earth-like exoplanets, the promise of astrobiology — namely, alien life in some form — seems closer than ever to reality. Yet what if aliens are already here on Earth, not as otherworldly visitors but alternative organisms, separately evolved and existing in a shadow biosphere?

That’s the question asked by Sarah Scoles in a new article in Aeon Magazine. To explore this possibility, Scoles first checks in with Carol Cleland, a philosopher at the University of Colorado, Boulder, who’s also affiliated with the NASA Institute for Astrobiology. Cleland coined the term “shadow biosphere” as she hypothesized whether forms of life might have evolved on Earth that don’t adhere to molecular biology’s central dogma. How might we find such organisms, Cleland asks, if all our methods — PCR, genetic sequencing, cell culture, and so on — will only detect familiar, DNA-based life? Cleland suggests closer examination of such anomalies as desert varnish—a residue found on desert rocks containing elements not appearing in the rocks themselves, so far unaccounted for by any known chemical or biological process. Along with looking for such organisms or their traces, you could also try building them, as geneticist George Church and astronomer Dimitar Sasselov are attempting to do using base molecules that are chiral mirrors to those known to exist in nature. Scoles also discusses a notable near-miss in the search for alternate life: the organism GFAJ-1, found in California’s Mono Lake in 2010, that seemed able to use arsenic in place of phosphorus in its DNA, but turned out simply to be a regular, if hardy, bacterium.

Is the known system of DNA, RNA, and proteins the only possible basis for life? Or, could the conditions that gave rise to this molecular marvel have also produced lifeforms with a different operating system? In confronting such questions, we look both to the potential for extraterrestrial life and to the continuing mystery of our own origins.

 Source: Aeon Magazine

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