Our universe holds over a hundred billion galaxies, each containing many billions of stars. We now know that many of those stars are orbited by planets, and it’s almost impossible not to conclude that, even if just a tiny fraction of one percent of those planets lie within in a star’s habitable zone, the universe must be teeming with life. And surely some of those life-supporting planets have given rise to complex, multicellular and, occasionally, intelligent life.

On the other hand, consider how incredibly improbable our existence is. As scientists come up with theories to explain the peculiarities of alien solar systems, their conclusions point to the possibility that our early solar system was a pretty chaotic place. Jupiter may even have gone walkabout in its early days, wreaking havoc on the orbits of its smaller brethren and setting up collisions with comets, asteroids and even other planets. And it could do again.

Just having a planet of the right size in the right place, with a stable orbit and a moon to help keep it steady on it axis, rotating at the right speed so the sunny side doesn’t get too hot or the shady side too cool, with liquid water, a protective magnetic field, the right blend of atmospheric gases and the other critical conditions needed to kick-start primitive life is unlikely enough. But the right conditions then need to persist for billions of years if even the most basic forms of multicellular life are to evolve. Earth has experienced cataclysmic events – large scale volcanism, asteroid impacts and the like – that have nearly wiped the planet clean of life. The fact that life persisted may be evidence that it is incredibly resilient. Or it may simply be that life on Earth has been incredibly lucky.

At the level of species and individuals evolution is partly a lottery. It isn’t just about survival of the fittest; it’s also about survival of the luckiest. Without the impact that wiped out the dinosaurs the world would be a very different place, and if we were able to do a rerun of evolution it would yield different results. There are many millions of species on Earth, yet only one exhibits our type of intelligence. Rather than being inevitable, we humans are highly improbable.

Yet here we are, endowed with the mystery of human consciousness and able to comprehend something of the universe and our place in it. Looking out we can contemplate the possibility, or even the probability, that we are alone; that in the entire universe life is restricted to a thin layer of Earth’s crust and a smear of atmosphere just a few kilometres thick. We can appreciate and be awed by the amazing richness of life that shares our tiny sanctuary, and we can understand the threat that we pose to it.

Even if life is sprinkled throughout the universe, we are astoundingly rare bundles of self-aware atoms. We are, without a doubt, incredibly lucky not just to be here, but to be able to marvel at all the living wonders of our world. Isn’t that reason enough for us to want to preserve our rich legacy, rather than be the agents of its ongoing impoverishment?

If we really value our minuscule planetary gem  we will need to try a lot harder to not further stuff it up.

Image: NASA via Wikipedia (public domain)