There’s no doubt you have heard about the plethora of planets which are Earth-sized planets in habitable zones capable of housing extra-terrestrial life. In fact, there are hundreds of billions of potentially habitable planets so it’s hard not to ask “are we alone”.
Surely by now with this many possible planets, we would get some sign or spot something, anything.
Our continuous hope in discovering life beyond ours could be naively optimistic. Many scientists and commentators equate more planets with more extra-terrestrial life. However, this is ignoring the violent and unstable early formation and evolution of rocky planets much like ours. With this considered, the logical conclusion is then that most of the planets we have found may house ETs. Except, they are most likely extinct fossil microbes. On our own planet, we find it hard to piece together the remains of the long dead dinosaurs, so it’s unsurprising that these fossilised microbes are not easy to detect by the remote sampling of exoplanetary atmospheres.
In research published in the journal of Astrobiology, it is argued that early extinction is the cosmic default for life in the universe. This is because the earliest habitable conditions may be unstable as discussed before. The “Gaian Bottleneck” model suggests planets need to be inhabited in order to remain habitable. Hence, even if the emergence of life is common, its persistence could be rare. Looking for evidence closer to home, Mars, Venus and Earth were ore-similar to each other in their early infancy. After 1.5 billion years of formation, Venus started to experience runaway heating and Mars experienced runaway cooling. If Mars and Venus once held the seeds to life, that life would have quickly died off. Let’s just say Earth got lucky, the fact remains that runaway freezing or heating may be the default fate of planets which are habitably unstable. Why is this the case? Well, large impacts and huge variation in the amounts of water and greenhouse gas can induce positive feedback cycles that continue to drive planets away from habitable conditions. Hence, Earth in its infancy was able to successfully supress this positive feedback loop and enhancing negative feedback loops.
So how was the negative feedback loop enhanced? As unsatisfying the answer is, it is more than likely down to plain luck. Earth was lucky to house microbial communities which prevented the runaway conditions. So, the answer to are we alone in this universe? Well, it’s a no if you count the dead microbes on the millions of discovered exoplanets. It’s a rather unsatisfying answer for now but I think there is something more we can take from this. It’s awfully humbling to know that the formation of life as we know it today started with a bit of luck. 1 degree colder and we might not be here. So perhaps whenever we feel like the world is against you, just remember that the world has allowed us to exist. It just goes to show with a bit of luck and constant persistence, beautiful things happen. Earth is one of the products of the universe’s persistence and overcoming your own adversities is just another product.