Our biosphere is the culmination of every ecosystem or population of living things on Earth. It is, literally, the sphere of life. Every living thing we know is part of it. But what if there was another group, sharing the planet, who didn’t belong? A hidden world of Earth-bound aliens, as different from us as anything we can find on any other planet in the universe. Tucked away in the shadows.
The shadow biosphere is an interesting theory of about the origin of life on Earth. There are a couple of different theories of how exactly life got started, however, we’ve all heard of the primordial soup; molecules combined in a pocket somewhere, which led to DNA, which led to cells, leading to, well, everything.
However, there is nothing to say that it was that straightforward. It’s quite possible that this had to start multiple times. Maybe the cells didn’t divide quite right, maybe the molecules were just too unwieldy or expensive. So it’s possible that many different lineages cropped up all over the world.
Eventually one lineage (ours) proved to be the most stable and strongest and spread out for the next four billion years. If other lineages did exist, they would have been wiped out by the competition or changes in the ecosystem (the early earth was a much, much different place).
But it’s possible that they weren’t wiped out. While our lineage, our biosphere, is certainly the dominant one, it’s possible that these shadows continued to exist in places our lineage simply could not go. These would be like the extremophiles, living in extremely acidic, or hot, or salty environments.
Earlier this year a NASA scientist reported to find strange bacteria in Mono Lake, California. These bacteria used arsenic as a building block for their DNA, something unique in our world. For a while it was thought that this could be an example of the shadow biosphere, but ultimately, scientists have decided it’s most likely an adaptation of our own lineage, not something completely different.
So far the shadow biosphere is still unproven. However, it is interesting to consider how we may be harboring aliens on Earth. And as we start planning on sending probes to Europa and other moons and planets to look for aliens, many scientists are turning to looking in the shadows.