Aug 1, 2023
“It may turn out that life is every bit as ubiquitous in the universe as it is on Earth, but it may also turn out that we are utterly alone.”
Since I was 5 years old, it has scarcely occurred to me that we might be alone in the Universe. We live in a cosmos made up of billions of galaxies, each housing billions of stars. It is ludicrous to think that ‘life’ has occurred only on one rock in one solar system in one galaxy.
When my children were young, we’d spend hours speculating on which moons of which outer planets were most likely to harbor life…and what that life might look like. And Mars? Of course, we’ll find life there; the only question is whether that life will be extant…or extinct.
For 70 years, extraterrestrial life was a fixed star in my firmament, a premise in my logos. But that was then! Now don’t get me wrong, I still believe it is absolutely possible that we will discover incontrovertible evidence – perhaps before I finish this article - that life arose independently somewhere else in Universe. But I no longer take that for granted.
From childhood through middle age, my belief in the existence of extraterrestrial life marked me as a bit of a kook. But over the last 15 years, the rapid discovery of ‘exo-earths’ and the apparent ubiquity of precursor organic compounds has moved public opinion sharply in my direction. Except I’m not there anymore. I’ve moved on. Here’s why:
All life on Earth is a product of DNA, but that strange double helix appeared only once in Earth’s 4-billion-year history, and that was about 3.5 billion years ago. Every single life form on Earth today, every species, every cell is descended from that one DNA molecule.
Incredible…but so what? Well, it took a mere ½ billion years for the first primitive DNA molecule to synthesize; in the 3.5 billion years since, not a single self-replicating molecule has formed independently anywhere on Earth. Why not? If the progression from organic compounds to self-replicating molecules is semi-automatic, why did it happen here only once?
Our study of terrestrial life forms has shown one thing above all else – life is resilient! You can’t kill it, no matter how hard you try. Of course, you can easily kill a single organism with a tug on a trigger. But life itself? No way!
Consider the evidence. A single DNA molecule is responsible for the 2 million ‘known species’ in Earth’s biosphere. (The total number of species may be as many as 10 million.) Even more significantly, life thrives virtually everywhere on Earth: arctic, tropic, water, land.
Living organisms can breathe oxygen…or carbon dioxide…or methane. Some organisms, like the Water Bear, can apparently survive for long periods without access to any breathable gas. Freeze an organism for centuries and, under the right conditions, you may be able to revive it. Life – you just can’t kill it! So if life had emerged more than once on Earth, all forms would likely have survived…at least long enough to leave fossil records. So where are they?
The Martian climate is not particularly hospitable to Earth-like life but, given their track record, there is no doubt in my mind that terrestrial life forms, once introduced onto Mars, would quickly adapt and survive indefinitely.
So, one of three things must be true: (1) There is not now nor has there ever been any indigenous life on Mars, (2) there once was life on Mars, but now it’s extinct, or (3) there are living organisms on Mars today.
We’ve ruled out #2. If #3, we should have found incontrovertible evidence by now. We have littered the Martian landscape with scientific debris. We even have a helicopter flying around in the ultra-thin atmosphere. So far, nothing.
But #3 has an even bigger problem: While Universe may be stingy with life, it appears to be generous with intelligence. While life ‘evolved’ on Earth only once, ‘intelligence’ emerged independently on multiple occasions in multiple forms, among primates, avians, cephalopods, insects, trees, etc. Could it be that intelligence is ubiquitous and life unique?
Sadly, this leaves us with #1: we won’t find any playmates on our ‘twin planet’.
Beyond Mars, we’re actively searching the rest of the Universe; we’re broadcasting our EM messages into space…but no one is returning our calls. And apparently, nobody is trying to get in touch with us either. We have searched in the most likely spots: the Martian soil and the EM spectrum, and found nothing.
So, I propose a new SETI paradigm: If life had evolved independently, on Earth or elsewhere, it would have survived and it would be intelligent. The galaxy-wide search for extinct microorganisms is doomed to failure.
The most respected contrary argument is based on probability theory: “It is infinitesimally probable that life emerged once on Earth and nowhere else.” This argument is persuasive…but false!
Suppose I pick a card out of some deck and the card I pick happens to be red. I might be tempted to assume that all the cards in the deck are red, and they very well may be. But maybe half are red. Or maybe none of the remaining cards is red. Perhaps every card in the deck is a different color.
We have no idea! We have a single data point. We don’t know if the value of that data point is universal or unique. Without more information, all possible arrangements must be considered equally probable. We need at least one more data point to be able to reason probabilistically; but at the moment, we don’t have that 2nd point.
So, while it may turn out that life is every bit as ubiquitous in the Universe as it is on Earth, it may also turn out that we are utterly alone.