The clues to finding alien life could lie in Earth’s deep past | Artificial intelligence
FEW discoveries could be bigger than detecting life on another planet. Whether it is a rocky ball or a giant cloud of gas, hot, cold, or somewhere in between, we aren’t picky: so long as a world has life, we want to find it.
For as long as we have searched, we have had one image in mind: Earth. It might seem like vanity, but our focus makes a certain amount of sense. After all, Earth is the only planet in the universe that we know for a fact supports life. Even if faraway exo-Earths don’t have oceans, continents, rainforests, deserts and polar caps, the long-standing assumption is that they will still be familiar in certain ways. There will be water on the surface, oxygen in the air, possibly even vegetation on the land.
But Earth hasn’t always looked the way it does now. In the 4.5 billion years our planet has existed, it has experienced dramatic transformations: ice ages and warming periods, times when the atmosphere was impossible to breathe, when large areas were desert, or when lush tropical forests hugged the poles. Throughout the vast majority of this turbulent history, life has somehow clung on.
If, armed with a spotters’ guide to the world we inhabit today, we found exoplanets resembling those early Earths, would we even recognise them for what they were? Maybe not. We know how to seek comparatively advanced signs of intelligent life, such as cacophonous radio transmissions and the bright lights of megacities. If a planet has less sophisticated inhabitants, however, we must rely on identifying other signatures …