It’s not crazy to think that Earth may be home to descendants of an alternative biogenesis, one that produced organisms current technology is unable to detect. These potential life forms are would-be residents of what has been termed the shadow biosphere—alien life forms of unknown origin and unfamiliar construction that have been thriving on this planet since its formation.
The word shadow is used to describe this phenomenon because the only clues that an ancillary biosphere might exist are the traces left behind by its potential inhabitants on environmental features that are measurable with currently available technology. This is why proof of shadow microbes is so elusive.
Under a microscope, many simple organisms we understand to be different, such as archaea and bacteria, appear remarkably similar. Finer distinctions are drawn, however, by using more sophisticated tools. For instance, microbiologists can now use genome shotgun sequencing methods and staining techniques like DAPI to discover more novel life forms than ever before. But these tools are still limited in scope. Another dilemma is that we can currently cultivate less than 1 percent of recognized microbes in the lab, and microbial communities are extremely diverse.
Considering how life is thought to have initially emerged on Earth, it makes sense to think that there are multitudes of life forms yet to be discovered.
Read the rest of this interesting article by Carol Cleland, a philosophy professor at the University of Colorado, Boulder – here Looking for Earth’s “Shadow” Biosphere, Where the Aliens May Be Hiding | Motherboard.