(Here’s an interesting analysis of the so-called Drake Equation.) And our particular planet, as you may have noticed, is the worse for wear, after centuries of humans killing off other species, deforesting vast swaths of the continents, and pumping such astonishing quantities of pollutants into the atmosphere that they’re rapidly altering the climate. If an alien civilization is sufficiently advanced to travel here from another star system, surely they could find a planet to invade that’s still under warranty.
So if aliens ever are going to invade Earth, they’ll need a pretty good reason. Our feverish, paranoid brains have dreamed up 10 likely possibilities.
- Earth has some unique resource that they can’t find closer to home. Who knows, maybe scandium, a mineral used to make aerospace components, is rare elsewhere in the cosmos. We’ve wiped out civilizations for less.
- They want to prevent a mass extinction of other species. Maybe extraterrestrials see us as the equivalent of the yellow crazy ant, an invasive species that is wiping out Easter Island’s red crabs. Whales, dolphins and butterflies are a lot cuter than humans, you must admit.
- They want to enslave or domesticate us. Reality TV contestants notwithstanding, there’s ample evidence that humans can be productive, with the right motivation and guidance. We might make excellent pets, as well.
- They want us for food. There’s genetic and physical evidence that our ancient ancestors were cannibalistic, so human flesh apparently has some nutritional value. The Earth’s burgeoning human population has the potential to provide billions of meals to Aliens, just like some hamburger chain whose name we won’t mention.
- They want our DNA. There are numerous sections of the human genome whose function is unclear. It could be that some of these genes might have some value if transplanted into an extraterrestrial species.
- They want to wipe us out because they’re afraid of us. Humans are small and physically puny compared to many other terrestrial species, but they make up for it with their prehensile thumbs, highly-developed intellects, and propensity for brutal violence. If aliens learn of our lengthy history of wars and violent crime, they might decide that it’s prudent to eradicate us before we develop the technology to project our animus on an interstellar scale.
- Earth is in the way. We seem to remember that in Douglas Adams’ A Hitchhiker’s Guide to the Galaxy, our planet was demolished to make way for an interstellar expressway.
- They want to test their weaponry. Remember that in 1937, German bombers destroyed the Spanish town of Guernica not so much to help the Spanish fascist cause, but as a preparation for a future war against the French, British and Americans. Maybe the aliens want to see how well their heat ray guns work in a real situation.
- They want revenge. Some have speculated thatlife on Earth is the result of ancient seeding by some extraterrestrial civilization. It’s not inconceivable that some rival bunch of aliens might hold a grunge against us as a result.
- For amusement. Humans’ capacity for senseless cruelty toward vulnerable species is well-established. As the Greek poet Bion noted in 100 BC, “Though boys throw stones at frogs for sport, the frogs do not die in sport, but in earnest.” It could be that to some alien species, we’re the equivalent of those frogs.