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Your average Invading Alien Species shows up and plans to invade Earth. They are Default Dumb Movie Aliens and don't have nanotech, AI, space habitats, diplomatic abilities, self-replicating factories, slaughter bots, or anything else one expects a Real Interstellar Empire might bring to the table. Their plan is to invade the earth using infantry (because The Author can't be bothered to learn about combined arms tactics), to enslave humanity, and to turn Earth into a colony. This is known to us because The Plot requires us to know it.

You know how this usually goes. The Plucky Hero wins because the Aliens never heard of cyber security. But what if the World Governments decide that there is no hope and Subvert The Expectations of the aliens by committing collective suicide while Trashing The Place? Think of this as a final, species level f-you salute.

How hard is it to do this? My current best idea is to use salted nukes/cobalt bombs, deliberately releasing toxic chemicals and mass producing hydroflourocarbons*. Is this the best strategy? Assuming we commit 30 percent of the world economy to this for a year, how bad would the damage be? The ideal outcome would be toxic, irradiated waste lands under a Venus like atmosphere.

Edit 1: The Aliens want to take Earth intact. They need our environment because The Plot requires them to require it. We know that ruining the Earth in the manner described above will deny them all their objectives. Don't think to deeply about how the aliens work or think, The Author doesn't do that and neither should you.

*I meant sulfurhexafluoride.

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    $\begingroup$ With such a subversion, the Hero and a couple Chosens should escape to alien Whatever-Ship, reach their homeland and go DOOM on them. Probably reinstating humanity on their ruins after everything gets down. $\endgroup$
    – Vesper
    Commented Feb 10, 2023 at 11:17
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    $\begingroup$ The answer can be approached from several angles depending on what the aliens want from the earth. Wiping all of humanity would be an easy-ish feat to accomplish, and most/all life on earth could not be a far-cry either. But if the aliens don't care about breathable atmosphere, aren't affected by "human" toxins or radiation, and only want earth for its natural resources or precious metals, it needs to be approached differently. You don't want to hand the aliens a nicely pre-terraformed planet on a nuclear platter. $\endgroup$
    – Plutian
    Commented Feb 10, 2023 at 11:27
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    $\begingroup$ @TheDyingOfLight Thank you for the clarification, it should set a decent enough premise for the question to be answered. Also I should note I thoroughly enjoy your liberal use of handwavium and "Plot". All too many askers take themselves much too seriously. $\endgroup$
    – Plutian
    Commented Feb 10, 2023 at 11:43
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    $\begingroup$ @A.bakker I know him. Yeah, the styles do overlap here. 😅 $\endgroup$ Commented Feb 10, 2023 at 15:07
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    $\begingroup$ Voted to reopen. The linked question explicitly states that it's fine if life gets reintroduced from an outside source. This question explicitly forbids that and indeed the entire point is to make the planet useless to outside sources of life, i.e., invading aliens. Please do not label "related" items as duplicates unless they actually are duplicates. $\endgroup$
    – JamieB
    Commented Feb 12, 2023 at 5:10

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If we can't have it, you can't have it either!

This is exactly the level of petty that the human race is, and if faced with an unwinnable war and insurmountable opposition, this is exactly what I would expect them to do as their "Last hurrah".

For your handwavium to work, all the aliens need within the premise of your question is this: (near) infinite reinforcements.

Sure, humanity could fight back, take a battle or two, make machineguns go brrrr. But there's just an infinite amount of the buggers. It becomes increasingly obvious that even if we go down fighting, we cannot "win" against the aliens Zapp Brannigan-style of combat. So we want to go down the pettiest way possible of course.

As per your question: "My current best idea is to use salted nukes/cobalt bombs"

Sure, we could pop all our nukes and nuclear power plants, but that's boring. The aliens recognise a lost cause when they see one, so they leave and go conquer another civilisation instead. Instead of destroying the earth instantly, it would be infinitely more middle-finger-ish of us to poison the earth slowly. This would make the aliens think they have won, and waste copious amounts of their time trying to harvest a dying planet while being powerless to save it. This would of course delay them from moving on to another conquerable world and set back their race as a whole. Or at least get one overworked alien overseer fired for not meeting their quota.

Your other ideas would hold more merit for a slower, yet equally irreversible death. Which is, of course, a better way of sticking it to the alien menace.

I quote "deliberately releasing toxic chemicals and mass producing hydrofluorocarbons. Is this the best strategy?"

Most likely, yes. We spend all our money on supersizing and automating our production of Chlorofluorocarbons, and release them into the atmosphere. (Note that Hydrofluorocarbons were invented to replace the much more dangerous Chlorofluorocarbons, so we'd have to go back to basics for this one). At the same time we unearth and burn as many of our fossil fuels as possible. Within moments our ozone layer and atmosphere will be irreparably ruined, and UV-radiation form the sun will take care of the rest for us.

Of course humans have extensive experience with this already, and getting humanity behind this approach wouldn't even be too hard. All you'd need is a copious amount of misinformation and lies, and we'll get right on destroying ourselves. I doubt you'd even need to tell them why. And with humanities current approach, I might even doubt the aliens make it here before all of this happens regardless.

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    $\begingroup$ I dunno, does any of this ruin the earth permanently? Space faring aliens may be very patient. If the earth has been "cleansed" of the filthy biological contaminants that called themselves "hoomans" and the planet needed a couple hundred thousand years to settle down, that might be okay with them. $\endgroup$
    – JamieB
    Commented Feb 10, 2023 at 15:27
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    $\begingroup$ @JamieB While the definition of permanent can subjective, the question explicitly states "The ideal outcome would be toxic, irradiated waste lands under a Venus like atmosphere." I do believe that is mostly achieved here, whether this can be considered permanent (enough) or not. Shy of splitting the earth apart altogether I don't believe anything we could do would be considered that kind of permanent, but this would be beyond the scope of the question. $\endgroup$
    – Plutian
    Commented Feb 10, 2023 at 15:44
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We only tried to kill the aliens.

Since the aliens have been foolish enough to send wave after of wave of infantry against us, they have provided us with an endless supply of genetic samples to study. Even though these alien lifeforms may have the same basic requirements as human, there is inevitably some difference between human and alien biology to exploit. If we can make herbicides that distinguish between crabgrass and wheat, then creating a xenocide that can distinguish between Earth biology and alien biology is not that hard.

Last year, a pharmaceutical company had an AI invent 40,000 chemical compounds that are suspected to be hazardous to human life in just 6 hours. Do the same sort of test on some alien genetic samples, and all you have to do is weed out all the chemicals that might also be toxic to Earth life and anything left can be quickly tested on the many platoons of aliens for actual lethality. Whatever chemical gives you the best bang for your buck, is the one you use. Thanks to recent creepy advancements in AI, your humans could go from theory to selective bioweapons in a matter of days.

But we didn't have time for clinical trials...

So we've made a bioweapon the kills aliens: CHECK! ... but the OP requested suicide: Not Check? You see, the problem with the OP's presumption is that we can and will trash the place on purpose all while devoting massive resources to fighting an actual war. We might unleash a nuclear holocaust or something of that nature, but even detonating the entire world's nuclear arsenal is going to at most make the world on average, unpleasant, and any toxin we try to manufacture might kill us all long before it reaches sustainably toxic levels world wide, again cutting our trashing off at mildly unpleasant levels before we can do any truly serious damage, but if the toxin is a thing we have a very high relative resistance too, then we can win the war first (putting us on less of a restrictive timeframe), and continue to make a hell-of-a-lot of the stuff before we realize that we've poisoned ourselves into annihilation.

The toxin kills humans too, but only by a very slow and unexpected vector so by the time we realize there is a problem, we've already dumped billions of tons of the stuff into the air making Earth so inhospitable to alien life that they will wish they were landing on Venus if they ever come back. The toxin of course kills us all off eventually, but what was just enough to be our undoing is millions of times what the aliens can sustainably take, so even if the chemical slowly breaks down or settles into various sequesters over time, it will have to go through many many half-lives before the Earth becomes non-toxic enough for the aliens to return. And since this chemical is fictious instead of a real chemical with properties your readers can just look up, you can say it will last as long as you need it too. Need Earth to still be a death world to these aliens 50,000 years later? No problem, because it is if you say it is.

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  • $\begingroup$ HA! That actually sounds accurate, and something we would really do, or end up doing. $\endgroup$ Commented Feb 14, 2023 at 18:51
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First, we don't have any of these:

  • Planet DeorbiterTM 3.0 - Planet smasher version
  • Supernova gunTM - Free your hydrogen energy ©
  • Super-duper ultra matter-antimatter planet converterTM
  • Pocket black hole creatorTM - Release your darkest dreams ©

We need to work with what we have as today. And here are our weapons, and we can produce a lot of them:

  • Fire! Fire! Fiiiiire!
  • Atomic bombs
  • Cobalt bombs
  • Hydrogen bombs
  • CFC
  • Coal
  • Oil
  • Mercury
  • Arsenic
  • Lead
  • Microplastics
  • Herbicides
  • Junk

So, here goes the script.

  1. Aggressively mine all the coal and oil as possible and burn it all!
  2. Orange agent and other aggressive defoliants should be produced in mass and spread out over everything that is green.
  3. Mine and purify the most mercury, lead and arsenic as possible, and release it all over the soil, specially in forested areas.
  4. Burn down all the forests!
  5. Release as much as CFC as possible. We will need large-scale CFC factories happily throwing all that CFC in the atmosphere.
  6. Release as much sulphur dioxide, lead and methane smoke as possible in the atmosphere.
  7. Aggressively get the most salt as possible from the oceans and drop it over fertile land.
  8. Build a canal draining lake Victoria and lake Tanganyika right into the Indian Ocean.
  9. Build a canal diverting the Nile from Khartoum right into the Gulf of Aden.
  10. Close the Gibraltar strait with tons and tons of concrete and stones until a wall several dozens of meters high blocks the Mediterranean Sea.
  11. Close with concrete the Suez canal.
  12. Close with concrete the Bhosphorus and/or the Dardanelles strait.
  13. Dig a deep canal from the Black Sea to the Caspian Sea.
  14. Dig a lot of deep and large canals to drain the Great Lakes as quickly as possible and also avoiding them from refilling (including even lake Winnipeg).
  15. Nuke ice caps in order to force calving, avalanches and ice meltdown.
  16. Dig deep into tectonic faults and nuke them.
  17. Remove undersea soil and sand from atolls and corals and drop that sand in freshwater lakes.
  18. Burn oil and coal in open pits on ice caps.
  19. Concrete Denmark to Sweden closing down the Baltic Sea.
  20. Fill the sea around Indonesia with sand and rocks took from elsewhere and concrete everything until there are land bridges connecting Sumatra, Singapore and West Malaysia to New Guinea, Philippines and Australia, making all of them a very weird and long peninsula of Asia instead of an archipelago. So, the waters from the Indian Ocean will need to travel all around Australia in order to reach the China Sea. But we can go further and also connect China to Taiwan and Taiwan to Philippines, making all the sea there isolated seas that would start to dry up and shrink making that a very new large peninsula of Asia.
  21. Close the Bering strait too.
  22. Create a land bridge from Djibouti to Yemen and another from Dubai to Iran.
  23. Create a deep canal draining lake Baikal into the Okhotsk Sea.
  24. Get the excess sand from Sahara, Arabian and Australian desert and dump them in places that used to be green, mostly into the Amazon forest, Congo forest, US midwest, Europe and China.
  25. Dig a deep canal to divert the Mississippi river from the Spring lake into the lake Michigan.
  26. Any remained land places that are still more or less habitable to vegetation should be nuked and "chernobylized".
  27. Produce microplastics in a scale as never seen before and dump everything into the oceans.
  28. Mine dangerous green-house natural gases like methane and let them leak in mass into the atmosphere.
  29. Unbury all the junk that we ever produced and buried, let all the gases escape, burn all the biodegradable stuff and drop the non-biodegradable part into the seas.
  30. Connect with land bridges Busan in South Korea to Tsushima Island, Iki Island, Kyushu, Honshu, Hokkaido, Sakhalin and mainland far-east Russia. This will make the Japan Sea an isolated sea that will shrink like the Aral Sea did.
  31. Connect with land bridges Hokkaido to the Kuril islands until Yamchatka, so the Okhotsk Sea will also become isolated and eventually shrink.

This will trigger a disaster comparable to some known mass extinctions. But even with all of that, in a few million of years, nature would likely be able to recover and go on, with or without us and the aliens.

Also, the land bridges serve an interesting purpose: To kill archipelagos and make lakes and interior seas shrink (even the Mediterranean Sea). This will make the continents more arid and more similar to Pangea. Europe-Asia-Africa will become much more a single continent than what it is today. The Americas and much of Oceania including Australia would also be connected to Europe-Asia-Africa. Only Greenland, Antarctica, Iceland, New Zealand, Madagascar, England, Ireland and a few small archipelagos would remain detached from the NeoPangea.

Finally, if you want to:

  1. When the isolated seas already have shrank down significantly and the aliens are already landing, nuke some land bridges and let a deluge happen.
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It really depends on your (the Aliens') definition of permanent, because honestly very little apart from cracking the planet into bits will truly permanently (ie forever) ruin a biosphere. The cobalt deposited in the environment by a salted cobalt bomb has a halflife of only ~5 years, so while it would make the planet uninhabitable, permanently wreck the biosphere it would not. CFCs break down over time (fairly quickly actually, as shown by the ozone hole repairing itself after only a few decades) so are only effective at tanking an ozone layer if continuously released. The ozone layer also has much less of a job to do protecting sea life, so even if you could get rid of it permanently if the aliens like it under water they might not even notice. Even the longest lasting "forever chemicals" break down over time, they are only "forever" on human timescales. And they (PFAS) are also not very toxic, so they wouldnt permanently ruin the biosphere either. Most chemical weapons that would give the aliens trouble (not reliant on earth biochemistry specifically, so things like chlorine gas rather than say, a nerve agent) are pretty reactive to have their effects, so they also wouldnt be very long lasting.

To truly wreck a biosphere you essentially need to sterilize it, down to the bottom of the deepest parts of the ocean. Bacteria have even been found pretty deep into the earth, just chillin in fractures in the bedrock doing chemosynthesis. All of that life would need to die for there to be no chance of recovery, because otherwise life, uhhh, finds a way.

We could weaponize life though, if we relax the constraints a bit then a very aggressive organics digesting microbe could essentially grey-goo the planet while being just as dangerous to the aliens as it would be to earth life. Or the traditional grey-goo (nano machines that eat everything and make more of themselves) could also apply, though they would be subject to potentially being "turned off" somehow by the aliens (an EMP maybe, for a fictional setting anyway).

There's also the route of not ruining the biosphere, just making it so difficult to use the land that the aliens dont want it anymore. There are places in the world today that are so full of land-mines and unexploded ordinance that no one goes there. If we had a bit of warning to prepare we could scatter all the nukes and beyond metric f---tons of conventional ordinance as land and sea-based mines everywhere. We couldnt actually get everywhere but the aliens would have no idea where was mined and where was not (assuming no scanning equipment, anyway), so would have to assume everything was. And removing those is expensive, time consuming, and dangerous. This way makes a lot of assumptions about the aliens not having the tech to easily remove the mines though, which a more realistic spacefaring empire would probably have (whether its just good enough AI/drones that the removal can be automated, or whatever else).

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Permanently ruining the earth would be pretty hard. I believe pollution, nuclear weapons, etc, will at best get you a few thousand years of ruining.

My proposal is deorbit the planet. You can find a number of topics that dealt with this to get some hints, though I couldn't find one that directly answered your question -- most assume far future tech, take thousands of years to accomplish, or are trying not to ruin the planet. In your case, we have modern tech, a short timeline, and we don't care if we ruin the planet because that's kind of the goal anyway.

I propose space missions to move asteroids that will slam into Earth. Moving the Earth itself is hard, but moving big asteroids and then relying on gravity to give them real momentum should be easier. If we can get the asteroids to slam into the earth at an angle that reduces our orbital speed, then we deorbit. The asteroids pretty well ruined the planet, but the orbital change will make it permanent.

I'm kind of relying on your statement that the aliens are pretty dumb. They basically just throw ground troops at a planet until they win. Space combat is not their thing (and maybe that's why they picked us to take -- they regarded us a non-threat in space combat). They can shoot down missiles coming right for them but it's not hard to slip past them with rocketships that are "not a threat". What are we doing with those rockets? Where are they going? The dumb aliens don't even care. Maybe we're fleeing. Great! Send more troops down!

Maybe we can get the moon in on it, too, or as an alternative. Smash something into the moon such that the moon gets deorbited into the earth. I believe that would ruin things permanently.

Other options could include "gray goo". Self-replicating nanotechnology that just consumes everything. That's a bit fantastical at the moment. So is deorbiting the planet, really, but I think moving asteroids is within our ability, and intentionally throwing them at the planet with specific impact angles seems feasible if we really apply ourselves.

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    $\begingroup$ This idea has the added benefit that even if the asteroid doesn't actually deorbit earth, the kind of destruction caused by an asteroid of the size that eradicated the dinosaurs is still quite substantial. Killing of all life forms bigger than a rabbit is already a good start for longterm ruining a planet. $\endgroup$
    – quarague
    Commented Feb 10, 2023 at 16:23
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    $\begingroup$ I'm fairly confident that you are significantly underestimating the energy involved in moving celestial objects. Robert Zubrin, who is not known for his conservatism when comes to space, considers an asteroid deflection mission to be amazingly hard, even with decades to deal with the rock. $\endgroup$ Commented Feb 10, 2023 at 16:28
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    $\begingroup$ This xkcd what if gives an idea of just how much mass would be needed just to move earth enough to offset leap seconds. what-if.xkcd.com/26 To deorbit take a large fraction (majority?) of the planets mass. However I don't know any other way to truly permanently ruin a planet. $\endgroup$
    – Goose
    Commented Feb 10, 2023 at 17:39
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    $\begingroup$ If you have the ability to alter the orbit of an object large enough that it's impact on Earth will "deorbit" Earth, then just cut out the middle-man and alter the orbit of Earth directly. $\endgroup$ Commented Feb 10, 2023 at 18:24
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    $\begingroup$ A useful reference for earthmoving: qntm.org/moving, qntm.org/data. These assume you want to move it close enough to the sun or Jupiter such that the tidal forces tear it apart; if you're willing to accept a less thorough (i.e. lazier) solution, you'll need less energy. $\endgroup$
    – Ray
    Commented Feb 10, 2023 at 20:47
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The only brute force way to 100% ruin a planet is to deorbit it. This would require nearly as much mass as the planet and would require a type 2 civilization, which probably has better plans than suicide.

However our goal is to ruin it for the purposes of the aliens. So why would aliens want Earth? The question mentions turning earth into a colony. A colony is useful when it can supply a resource. What does earth have that's worth fighting for? Not the common rocks, or the common gases, or water. All of those can be found in massive quantities around the galaxy.

If you're taking over planets, it's because you need something rare enough to require multiple planets to get what you need. Heavy elements. Every supernova only creates so much of it, and it tends to be very useful. If aliens needed a cosmic amount of any heavy element, it would explain needing to set up colonies in far away star systems. And luckily for us, this would be far more feasible than de-orbiting the planet.

Mine as much of every heavy element from the crust that aliens could possibly want. Launch into the sun or destroy. This would still be a massive operation, but could be done by a type 1 civilization.

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De orbiting the planet sounds like a good idea.

But How about deorbiting the moon? Many planetary functions rely on the moon and if the moon crashed into earth its game over anyway. (we already have impact craft technology but its time to refine it to be sure one could do a meteorite bombardment of the moon)

Regardless, the nuke idea is probably pretty good, but as Chernobyl has shown, wildlife can adapt and survive.

Either that or creating a perfect Von Neumann machine. (self replicating robots that eat anything to reproduce.)

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The question needs additional clarification/information.

If the aliens concerned have actually arrived in the solar system and are in the process of trying to conquer the planet there are ZERO options available to humanity for ending all life on Earth. There aren't enough nuclear weapons to do so (doped or not), there are no biological weapons that would do so and no other actions we could take like trying to induce a runaway green house effect that would end all life/destroy the ecosystem in anything baring multi generational time scales.

There is in fact only one sure way of achieving this end and it requires the ability of Earth to access and operate in deep space. If the aliens are actually here that should by default be impossible simply because they control the 'high ground'. Nothing we launch would be capable of escaping the attention of a species with interstellar travel capable technology levels.

If instead the Aliens just sent a radio message saying something along the lines of 'We are coming to invade, resistance is futile, we will arrive in 25/50/100 years." Then perhaps we have time to initiate a space program designed to de-orbit a rock big enough to destroy all life aka the movie Deep Impact. Other than that we simply don't have the technical capabilities to end all life on Earth. Life is tough.

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Not hard at all. I think that in order to ruin earth, we just have to keep doing what we are doing. All we have to do is destroy the ozone layer and fill the earth with greenhouse gases in order for our big blue planet to turn into a second Venus. If you want to take the short way out, start a Nuclear World War. With just 100 nukes, you can basically destroy humanity one way or another. The nukes may make a huge cloud of dust and gas covering the earth for months, maybe even years. The cloud covering would impede the sun from coming down into earth so the world would freeze. Basically a new ice age.

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    $\begingroup$ It would take more than 100 nukes... ~2000 nuclear bombs were tested during the cold war without overly ruining the planet... but "luckily" we have a lot more than 2000 nukes sitting around just in case. $\endgroup$
    – Nosajimiki
    Commented Feb 10, 2023 at 20:17
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    $\begingroup$ Note that we stopped destroying the ozone like 20 years ago and it's healed quite a bit since then. Of course, that's easy to reverse if we wanted. $\endgroup$ Commented Feb 10, 2023 at 20:20
  • $\begingroup$ Earth cannot possible become second Venus because firstly, we are far further from the Sun, and secondly, we are not practically tidaly locked to it (unlike Venus). And it's higly unlikely that humanity wouldn't survive nuclear winter - sure, civilization would go to hell, but we would survive. $\endgroup$
    – Negdo
    Commented Feb 13, 2023 at 9:19

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