Today’s post is part of a special series here on Planet Pailly called Sciency Words. Each week, we take a closer look at an interesting science or science-related term to help us all expand our scientific vocabularies together. Today’s term is:
We are not alone on planet Earth. There are aliens among us. Their existence has gone unnoticed and unsuspected for millions of years.
Truth be told, I shouldn’t call them “aliens.” They evolved here on Earth, side by side with what we, in our arrogance, call “organic life.”
They’re everywhere. There’s a whole biosphere of these weird creatures sharing our planet with us. It’s called the shadow biosphere.
Not Crazy Talk
I first heard about the shadow biosphere on an episode of SciShow, and I’ve been seeing the term more and more lately. It seems like some sort of astrobiology buzzword at the moment.
The idea is that an alternative form of life could have evolved here on Earth, and we just haven’t discovered it yet. Maybe it lives in areas totally inaccessible to us, like deep beneath the Earth’s crust. Or maybe it’s so different from us that we don’t yet recognize it as a life form.
Personally, I take this as more of an astrobiology thought experiment than a serious hypothesis about life on our planet. It’s a way of reminding us how limited our understanding of life is and show how difficult it might be to identify alien life should we happen to find it.
You see, to determine if something is alive, we must try to identify ways in which it is similar to other living things. Does it move? Grow? Reproduce? On a more fundamental level, is it cellular in structure? Does it have a carbon-based biochemistry? A DNA-like genetic code?
But all these questions presuppose that newly discovered life forms will be similar to life forms we already know about. What if we’re dealing with a life form totally dissimilar to life as we know it? What if they’re non-cellular, non-carbon-based organisms that don’t have anything resembling DNA?
Why, such organisms might be so strange to us that they could exist all around us, even right here on Earth, and we wouldn’t know it. Or so this type of thought experiment may lead you to conclude.
Back to Crazy Talk
It’s not just a thought experiment. The shadow biosphere is real. It’s real, I tell you! Wait, where are you taking me? No, I don’t want to take my medicine. Are you working for them? Did the pet rocks send you?