Plenty of science publications and websites bring up this idea of Panspermia, a hypothetical mechanism by which life on a planet could be seeded, but does it really have any merit?
What’s important to note is that there is no such thing as an “armchair scientist.” What I mean by this, is that ideas are not inherently of value to the scientific community. They must pass through rigorous tests, and are considered on their merits. That’s why it is essential that we maintain the term ‘hypothesis’ when referring to panspermia. It is an idea that aligns with how we think the universe functions, but in terms of Earth, the evidence is just not there.
Biological scientists as well as paleontologists have traced back Earth’s evolutionary history back over the past three to four billion years, and the general consensus among the scientific community is that life began on this planet from a common origin, perhaps a single “organism” or self-replicating molecule. That’s more or less what life is: molecules—in our case huge organizations of molecules—that can reproduce themselves well. We as humans do so by having sex. Some organisms do this asexually; they just sort of split. There are benefits and costs to both but the evolution of sex is not yet fully understood.
It’s very difficult to study the early Earth, and could be likened to surveying a crime scene at a home that was torn down, nuked, and replaced by a different structure entirely. And it’s even worse because of the imposing time difference, but clues still remain.
My brother once commented to me on the breadth of a billion year time-span, saying something along the lines of,
“That’s long enough to make a tapestry out of a wall by throwing silly-putty at it.”
And that is the essential tool that brought us here from a molecular origin: Time.
So we can trace life back to proteins and amino acids—primordial DNA—just molecules that copy themselves. We don’t quite know where those molecules came from or how they formed, but we have some pretty good ideas! The study of the beginning of life is called abiogenesis; life from non life. Panspermia, on the other hand, suggests that life was seeded on earth from some extra-terrestrial origin, either by accident or by intent. But make no mistake, abiogenesis had to happen somewhere, though part of the admitted beauty of panspermia is that it only needed to happen once. Some of the questions that arise from considering panspermia can not be answered without contacting other life in the universe. We only have one example of a living planet so far.
So what gives the hypothesis of panspermia any merit at all? Well the first is through the intent; if life forms elsewhere in the universe, perhaps leading to some hyper-advanced civilization, it is conceivable that these beings might seed life on other planets for any number of reasons. For example, they may want to study the evolution of life and do an experiment on the survivability of species, etc. But one also has to question why they would do this, if they would have ethical concerns, or to what end they wished to progress, and one would also have to ask what evidence could there be to suggest this. Honestly, I am ignorant of any such evidence that would prove this short of direct extra-terrestrial contact, but regardless, no such evidence is apparent to us at this point.
The second is through the accident. This version of the idea has a little bit more promise than the pervious. It is conceivable that life evolved independently elsewhere in the universe, and microbial life was seeded—by accident—here on earth. This would likely have to be life that was within our own solar system, as stellar distances may be too vast for any living organisms to traverse.
Now let me try to clearly communicate something before I continue:
Panspermia is by no means a solution to the problems of the origin of life, it is merely a possibility, a thought experiment that could, with sufficient evidence, be a solution the origin of life on Earth. Scientists are very well aware that the origin of life would need to be accounted for regardless of whether it began on earth or not.
Continuing, one plausibility is that life began on our neighbor Mars, and then by some cosmic collision on the red planet, made an interplanetary journey to earth. This part of the hypothesis is fueled by the possibility that the early Mars environment was more hospitable to the formation of self replicating molecules than the environment of early Earth. Moreover, there are organisms living on earth that can survive in the vacuum of space.
Meet the tardigrade (also known as the water bear), a tough microorganism that can survive in extreme heat as well as extreme cold, can survive solar radiation, and indeed even the vacuum of space. To maintain honesty, it is worth noting that it can only survive in a vacuum for up to ten days. It is not meant to flourish in these environments, but it can survive them. The tardigrade is just one of many organisms that can withstand extreme conditions, so it is within reason to suggest such an organism could traverse interplanetary space, though this organism is almost certainly not the tardigrade.
But if this wasn’t fantastical enough, consider that there exist certain species of bacteria that can survive for thousands, even millions (yes millions) of years by going into a sort of hibernated state. If their environment is not very friendly, they will ‘turn off,’ and then reanimate once things become more hospitable.
So, let’s jump a little deeper into the rabbit hole. Imagine if such life mentioned above were to spark on a comet in the early solar system, and then happen to make a collision with Earth. There was some press buzz—though horribly misplaced—around the Philae comet lander some months ago, when the internet became convinced that life could have been on the comet. We’ve found no such life, but it is not entirely inconceivable that life could arise on a comet. This is unlikely, as comets have a relatively short lifespan. Life starting on a planet is our best bet.
Let’s get even stranger. Please keep in mind, this whole article has been centered on some very hypothetical and fantastic ideas, so each time I get weirder, I also get more unrealistic. Consider that humans have discovered that the organic molecules that make up much of life on this planet, can be found throughout the galaxy. Could life, maybe, have begun in the vacuum of interstellar space, and then simply fallen like manna from heaven?
We must continue to be skeptical and cautious as we consider these ideas. They have plausibility under extreme circumstances, but that by no means places them in the realm of reality, especially where our planet is concerned. The life on Earth, as shown by all the evidence available to us, evolved here. But the universe is so much more ancient than our planet, and more vast than our solar system. Could extreme circumstances be out there somewhere? We can certainly imagine.