In sci-fi books and movies, aliens are continually trying to conquer our planet. But this question is seldom, if ever, answered: why would beings from a distant, advanced civilization go to the expense and effort of journeying to Earth to mount an invasion? After all, Earthlike rocky planets are relatively common on the universe—scientists estimate that as many as 30 percent of sun-like stars have them, and the Milky Way alone, by various estimates has between 50 million and 10 billion Earth-like planets situated in the so-called “Goldilocks Zone” of their stars, in which temperatures are sufficiently moderate for life-sustaining water to exist in liquid form. (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.

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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.

1.    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.  

2.    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.

3.    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.

4.    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.

5.    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.

6.    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.

7.    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.  

8.    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.

9.    They want revenge. Some have speculated that life 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.

10.  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.

For more, be sure to tune in to When Aliens Attack this Sunday at 8P et/pt.


  1. Dr. Dimension
    May 23, 2011, 7:21 am

    Your reasoning is almost valid. It just has no historical underpinnings. We threw everything we had at the craft hovering over L.A. back in 1942, and (a)they did not shoot back (b)we did not prevail–they left-(recent experiments prove it was there). We can ignore history and continue speculating in bloodlust.
    You can fabricate a lot of fear-mongering if you don’t look at the facts. There are aliens, (thanks for considering that)and in spite of our history of trying to screw them in a power play, they have done nothing to us at a time when they should have…when nukes were in their infancy. Go back even further, and you will see that they have been noted throughout history, and they have always been benign. Ask Travis Walton. Hollywood took his story of healing and cooperation and turned it into a horror story. We won’t have too long to wait, I think. We can only hope the U.S. hasn’t developed weapons to equal them, because they aren’t going to let us continue warping the fabric of time-space with nuclear explosions.
    Then, there’s ten years of the Phoenix lights without incident from the craft….and no USAF response. What do they know? A lot of the wrong things are being said, but none of the right things. This show is pure propaganda.

    MI ... USA
    March 6, 2012, 2:04 pm



  3. Don't Spaz out Ron
    On a U.F.O
    January 2, 2013, 1:29 am

    if they have been watching us long before Man came to be then how where they watching us???

  4. derek
    May 15, 2013, 2:02 pm

    area 51

  5. ER
    June 14, 2013, 2:50 pm

    I’d say one good reason might have little to do with humans. The aliens could be at war with some other species and earth might just become strategically important. Also humans have proven to be adaptable warriors with a huge population. Properly trained and armed we could be made into the perfect disposable soldiers.

  6. GypsyJewel
    January 2, 2014, 9:45 pm

    Well watched to show and it was really good & insightful. Unfortunately when i heard the presidents voice I knew with out a doubt that this was truly science fiction B rated. You see what he would have said first was “Where is my teleprompter”, followed by, “The aliens have assured me that if you turn in your weapons that they will give us the cures to all major diseases”. What he fails to realize is that one of those diseases is “LIFE”. :) and then we would lose.

  7. Bull it
    May 9, 2014, 6:06 pm

    It’s unknown!

    – Couldn’t it be, that it’s them who colonized the human on
    – if they were so advanced and also different habitable planets
    The have a NATO sort of agenda or code to not interfere with
    uninvolved planets
    – who not to say that the human race issent the first intelligence
    race to invade. Cause who ever knew we could fly airplane
    – and we probley never make it that far.
    Mother Nature extinct the human race as it did with the Dino’s

    We just don’t know, or if it ever come that far

    “The truth is out there”

  8. […] Nat Geo list of reasons Earth might be useful to other life forms: […]

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  10. Zorbledork Tindunglehung
    August 30, 2014, 3:12 pm

    You’re all deluded. We have landed and we only wanted some peanut butter cups. We’ll be leaving again soon so you can go back to your boring lives stranded on this planet. Good day to you, Earthlings.

  11. MiskyWilkshake
    September 4, 2014, 1:37 am

    Point 1 is possible but unlikely. By all accounts Earth and our solar-system are not particularly unusual or unusually formed, there’s little evidence to suggest an abundance of anything in our solar-system that would be so rare as to necessitate interstellar travel to find.

    Two (while also possible) seems equally unlikely. There’s no reason to believe that aliens should have had any prior contact with any Earthling species – as such, there’s no reason to suspect any prior bias between species. While it’s difficult to speculate on the values of alien lifeforms, if they operate by any remotely familiar logic, then from a scientific viewpoint, humans are the most interesting and potentially communicable species on our planet.

    3 again seems possible but unlikely. Unless Earth is the only inhabited planet within the reach of alien life-forms, it’s likely that any species with the capacity for interstellar travel has it’s pick of lesser races to choose from when it comes to slaves and/or pets. Given the relative mediocrity of both our planet and solar-system, it seems unlikely we’d be first picked (just think, in terms of physical labour, we’re next to useless, and not only would we likely be out-performed by creatures in say… a more massive planet with greater gravitational force, but likely by many species already living on our planet such as horses and oxen – in terms of mental and or technological labour, we’re likely so vastly surpassed by any species that’s capable of interstellar travel that we’d be of absolutely no use).

    4 seems preposterous. The human body (like our planet and indeed solar-system) isn’t particularly special in any way. It’s made up much the same stuff as most other living organisms on our planet (and as far as our understanding of potential evolutionary routes towards what we understand as life goes, likely not too dissimilar stuff as would inhabit the lifeforms of most populated planets). It seems likely to me that any lifeform to which interstellar travel is trivial enough an endeavour to undertake for very slight variations in your meal would probably have evolved or developed through technology alternate means of nourishment (say, photosynthesis for example). This is just speculation, granted – but the logistics of an evolutionary tract which necessitated interstellar travel to ensure a stable food-source ever getting off the ground is pretty unfathomable.

    5 Seems possible, though I do have to interject that DNA alteration, splicing, etc are already within the scope of human technology – I’d wager that any race capable of interstellar travel would have little trouble creating DNA without stealing data from a host (though, I must admit, I have little to back this up: I’m no geneticist, and don’t have a clue as to exactly the difficulties involved in that, nor can I presume to predict the evolution of alien technology).

    6 Seems utterly impossible. I don’t see how a species which has barely left it’s own planet let alone it’s own solar-system and galaxy could be seen as a threat to any species that has. Likely, any species capable if interstellar (or indeed intergalactic) travel would view humanity as barely sentient, let alone dangerously intelligent.

    7 seems the most implausible of the list for the simple matter of just how big and empty space is. To quote Douglas Adams, “Space is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”

    8 is possible, though frankly, since their weaponry is likely designed for use either against their own species, or species which pose a threat, it’s likely that testing it on a race such as ours would be of little value. We don’t go out of our way to test nuclear weaponry on ants and germs – granted, some ants and germs get killed during our weaponry tests, but I refer back to point 5 – space is big; much bigger than our measly little planet, and there’s a lot less chance of collateral damage, unless the scale of the weaponry we are talking about is enough to wipe out entire galaxies.

    9 is preposterous pandering to conspiracy theorists and not even worthy of response or consideration.

    Frankly, number 10 seems the most likely to me, given just how inconsequential the human race (or indeed all the races on our planet) would likely seem to any race capable of traveling to and destroying Earth.

  12. Ash
    September 18, 2014, 11:10 am

    That absolutely rite……bt as shown in the film”independence”….aliens had already invaded………if they did ……can they be defeated by,the so called,our technolgy……..

  13. marc mc keown
    January 15, 10:19 am

    i takes just one case to be right on the ufo agenda , out of millions of sightings . they are here so are we

  14. rogert | Timeshare attorney
    united states
    January 16, 5:45 pm

    well , i believe that they already has taken our world

  15. […] Nat Geo list of reasons Earth might be useful to other life forms: […]

  16. tonyon
    February 11, 4:17 pm

    when aliens come Earth…goodbye religions and all its Lies

  17. tonyon
    February 12, 3:26 pm

    (1)…interstellar travel (to the third world)… we come in our ship from faraway…are reaching finally, that star they call Sun…our destiny that third planet is distinguished from the others aridly and barrens with its luminescent blue against the dark background of the Universe…now we are under its spell…they call the Earth…we pick up its broadcastings TV…we are hearing the stories that they tell…they speak strangely but we understand… We see at its inhabitants, the human beings very similar to us, outside… We have been studying them in their lifestyles, some in developed places with high level, and others in those others places to that they call…the Third World…suffering, hunger, malnutrition, war, calamities and horrors against the feeble… Are we dreaming or is it all real?… is it true?… We see at their leaders to they call religious…(Torquemadas that were “executioners” against the Human Beings in the Middle Ages with their Inquisition on behalf of their sanguinary gods, and still have the arrogance to put their secrets and sectarian religious symbols (channel TV Discovery Max, “secrets societies”) in the popular bank note 1 dollar, if anyone doubt who governs in the shadow the world… well fattened in their golden palaces… while…children perish converted into skeletons with some skin and eyes full of flies, in the arms of their horrified mothers who do not have even a glass of clean water to drink them… religious and political leaders that is purposely keeping the horror because WITHOUT POORS AND WITHOUT IGNORANTS THERE IS NOT RELIGION, not any religion. Have to separate between the worthy concept, strictly personal, believing in a Goddes or a God (wheat) and Humankind´s anxiety of Eternity;…from the manipulation and interested ancient Lie that is religion (the weed)… religions only are a Malign Tale for social control to serve at pontifices, monarchies and politicians… IT´S TRUTH THAT RELIGION IT´S LIE…

  18. tonyon
    February 13, 3:41 pm

    (2)…interstellar travel (to the third world)… we see its documentaries and films which are the 2 world wars that they have had, wars caused, not by the Peoples that only makes it´s to work, but by the conflicts of particular interests between the leaders of some European Empires and by some demented who thought they were “superiors” to the others and forcing everybody to defend themselves involved in the maelstrom…where they put in the balance the life of 1 single leader, against the lives of 200 million of Human Beings that cost those 2 wars…we see them jumping innocently from the deadly and muddy trenches, forced to the force by order of their inflexible “superiors”, to massacre them from enemy´s machine gun nest… while the causers of those wars…monarchs, politicians and of all religions pontifices in their golden palaces were eating partridges… We see that they not learn the lesson, are easily forgotten over time the horror of the bellicose past…carry in their genes the prehistoric fierce struggle for survival and hegemony, and are yet unable to realize that they are now a superior species of the Universe…lack them the Universal perspective for not have yet went in masses to Space and do not realize how small and yet how big they are. We see that and try to stop the war creating the UN, that honors them…

  19. tonyon
    February 15, 10:05 am

    (3)…interstellar travel (to the third world)… but get tired of living in “peace” that they are, instead of reaching at GENUINE PEACE not through of victory, what “victory”?, but through peaceable revolution of Justice, Truth and NO BELLIGERENCY OF ALL COMBATANTS LEAVING ARMS AND RETURNING TO THEIR HOMES, to organize a NEW WORLD UNITED WITHOUT NATIONS (only cities), braking the Planet overpopulation, with urgent sending of technology and all necessary to sub-developed areas as much as the WORLD EQUALITY IN ALL and then, and only then, get off finally Nations and Frontiers…with 1 single World Government for the flow of prosperity equal to the entire Planet taking care of all its inhabitants as if each 1 where singular and most important, only 1 Idiom and 1 single New Army without “superiors” (a person do not is superior at other person) for the safety and protection of Humankind in its expansion into the Universe with the Justice and Respect for flags… We see still some trying to separate politically from others to ensure their miserly privileges of own territory and language… We see now some to bring upon themselves severe altercations in sports stadiums…violence sponsored hypocritically by their own and sickly leaders “rossse tie” that are living from the People´s work and never stop making films of evilness, just look repugnant programming TV channels that are constantly putting their execrable owners, instead of using the media to heighten Intelligence, Equality, Goodness and Science…

  20. tonyon
    February 16, 4:05 pm

    (4)…interstellar travel (to the third world)… and all the films made with a ferocious, malign and subliminally infectious contents about the past, present and future, inciting them from those movies veiledly to violence…WHAT TO SEE IT´S WHAT TO DO…because that is how control them… CREATING PERIODICALLY ARTIFICIAL ECONOMIC CRISES AND WARS…so that the People could never live too well and peoples have no choice but to obey… VIOLENCE, POVERTY, RELIGION AND IGNORANCE… Like all Intelligent species have built their civilization from initial ignorance, but still have not realized that and NO more Lies, if they want to continue climbing has already been for steps Justice, Truth and Science. Unable to brake overpopulation of unique and contaminated planet who still have…we hear in the news: “in 2050 will be 10,000 million inhabitants”…”in 50 years there will be no fish in the sea”…”sea level is rising”…”a possible new ice age”…”unrelenting growth temperatures”…and stay so calm…never stop pouring million Tm/year contamination to the foul air, they are almost suffocating in cities…and blame to the Anticyclone… It seems that they will not be able to go beyond of their technological adolescence and out of the way of extinction, guided by ignorants leaders. After seen this…they have broken the spell, we had better go away to find another planet very far from… THE EVIL EMPIRE: RELIGION, ARMIES, MONARCHIES AND POLITICIANS… Goodbye Earth.

  21. What Is The Earth Worth? | Help
    February 16, 8:04 pm

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  22. sundar raman
    February 22, 2:31 pm

    its true means i want the real proof….
    who ready???????????????????

  23. sundar raman
    February 22, 2:32 pm

    Its true

  24. […] Nat Geo list of reasons Earth might be useful to other life forms: […]

  25. Celestial Angel
    Midwest of America
    March 15, 2:59 pm

    Species of Beings Aliens, the Extra – terrestrials from another Planet could invade Planet Earth to have breakfast, lunch, and dinner here on Planet Earth. The Species of Aliens could have plans to eat us as a Food Source. Human Beings on Earth eat other Human as a meal we Call Cannibals . We Human Being Species grow vegetable to eat at Harvest Time ,and maybe the Alien Species are waiting for the Human Being Species to reach over a few more Billions of People for their Harvest Time , the Invasion of Planet Earth for their Food Source to Eat Human Species of People .

  26. danfer0063
    April 30, 12:42 am

    The aliens have created an army of (human-alien hybrids) from the abductions to
    infiltrate every sector of our society to tear it down and take it over, the loss of
    our freedom and rights is because of them to lead the human race towards a
    new world order!

  27. Joseph De La Torre
    June 22, 2:12 pm

    I want to beleive.