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I'm writing a fantasy/sci-fi story. Imagine an alien race, about as advanced as any sci-fi alien race has ever been depicted in any REALISTIC medium. They're gonna target an earth-like planet. I need all human life, buildings, and cities eliminated on the surface so that the next civilization doesn't immediately realize it was recently a home to someone else. That said, we need some people who are underground to survive this 'attack' We can make these really deep if need be.

The planet is not the same as ours, but for the sake of convenience, assume it is exactly like our planet as it is today.

After the attack, the aliens will then, depending on the means of destruction, give the planet to a new human race replacing the old owners of the planet.

So basically, I need a method that would mainly clear the surface of the planet so that it could appear new to a, lets say, primitive race, but keeps people safe in bunkers, and I need it done within 10 years.

The alien race can then prep the planet for a new human race asap. They can speed along the rebuilding. We can allow the aliens to rebuild an ecosystem for the new humans if that's needs to be done. They could create land fills, throw trash into space, whatever they gotta to to make it presentable. They could travel the cosmos and repopulate/reintroduce the wildlife/ecosystem n whatnot. But if we can that can avoid this, great. This all depends on our method of destruction.

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    $\begingroup$ Do you mean all life, or all intelligent life? Or all animal life, but plants are fine? $\endgroup$ – Pasqueflower Jan 26 at 5:44
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    $\begingroup$ I did a large edit on your question and removed all your extra questions. Feel free to change it back, though I strongly suggest you save additional questions for followup posts. $\endgroup$ – Cyn says make Monica whole Jan 26 at 6:22
  • $\begingroup$ I also removed the [magic] tag because it's not applicable based on how you describe your question. $\endgroup$ – Cyn says make Monica whole Jan 26 at 6:23
  • $\begingroup$ When the new human race takes the planet, Ideally it would need some sort of ecosystem. Now, whether the eco system survives or is reintroduced by the aliens after the event, is one of the main parts of this event I've been struggling with. These aliens have the ability to bend time and go through wormholes with their super ships and travel around the galaxy in no time. Would they be able to snag up a few million bees, earthworms and all other essentials from some other planet in the galaxy? Or is there a way to keep all those things, more or less preserved? $\endgroup$ – halp Jan 26 at 6:28
  • $\begingroup$ Those are good questions but some of them are not within the scope of your first question. I suggest you focus on that first, or your question will be closed. Please do edit your question to put in your specs. For example, you say "annihilates all life" but you don't define it. Do you mean every microbe? That's going to be hard to replace (and make it impossible for underground humans to really survive). So decide if you want it to be all life, all land life, all plants and animals, all animals, all mammals, all large or intelligent life, all humans, etc. $\endgroup$ – Cyn says make Monica whole Jan 26 at 6:44
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Since this is a highly advanced race, a gray-goo apocalypse may be best. "Gray-goo" refers to self replicating nano-bots that eat everything in their path making more of itself until it covers the whole world. Then once the aliens are satisfied that humanity is good and dead, they just send a signal to turn it off, and their new people can start moving in the very next day.

Unlike a bio-weapon it can not be quarantined or vaccinated against. It can break through doors and walls to reach you or travel vast distances to find people in every remote corner of the world. Unlike Nuclear or chemical weapons, it does not poison the world. Also, because it is a programmable weapon, you can have it destroy life as discriminately or indiscriminately as you want so it can either just kill people or kill EVERYTHING down to the last microb.

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  • $\begingroup$ I been back n forth editing. I also need MOST evidence of a former civilization to be gone. If there is some evidence left behind, no big deal, could make things interesting. $\endgroup$ – halp Jan 26 at 8:08
  • $\begingroup$ The Grey Goo is very open to your own implementation; so, you could decide that it might turn all buildings to dust looking for wiring, pipes, and rebar to make more of itself. $\endgroup$ – Nosajimiki Jan 26 at 8:15
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Stick with Nuclear

The model that you're describing has been used many times in the past via a nuclear winter. If you need a human populace to survive such an attack, then you need only look at the Metro series of novels and books out of Russia to see how it would be possible for humans to survive a nuclear holocaust.

Ultimately, this fits with your intended timeline; most climate scientists calculate that a nuclear winter would only last for around 1 to 2 years, meaning that your native humans can still survive, if properly prepared beforehand.

Of all things, I'd stick clear of biological weapons. Reasons?

Well to begin with, there's only a 50% chance of any alien species having the same chirality as us, although it has to be said that those with the opposite chirality probably won't find earth an efficient target for colonisation. Secondly, biological weapons in a species capable of getting here in the first place are going to be devastatingly effective, and from the tone of your question you don't want that.

Thirdly, (and perhaps most importantly), if your attack has the intention of preparing the earth for alternative humans, then any biological weapon is just as likely to wipe them out as the native inhabitants.

An invading force doesn't need to create biological complications for itself, and any biological weapon that impacts humans is likely to impact the invaders as well, otherwise the planet doesn't make a good strategic target in the first place.

On the other hand, a nuclear strike against cities wipes out the majority of the population and keeps them from a source of supplies; food, energy, whatever they need. It means that some city folk may have prepared, but most (including the regional farmers) will die off during the nuclear winter.

So; strike, wait a couple of years, and colonise. Then, deal with the inevitable survivors from a position of strength as the years advance.

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  • $\begingroup$ Articles that cite that level of radiation are based on the amount of combat ready nukes today, which are only enough for about a 10% de-population of the planet. As you get closer to complete genocide, the amount of nukes you need goes up exponentially as you target more and more rural populations. You'd also destroy the entire ozone layer doing that which would significantly complicate re-colonization. $\endgroup$ – Nosajimiki Jan 26 at 8:42
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    $\begingroup$ @Nosajimiki Yes, completely agreed. But (unless I've completely misread the question) the real issue is how to wipe out most of the population while still allowing some to survive. This means that you really only need to nuke major cities to wipe out a civilisation rather than a species. Also, you're not relying on radiation to wipe out most of the planet as the nuclear winter will do that for you if you wipe out enough large population centres. It's the nuclear winter which is expected to last 1-2 years rather than the radiation sites. $\endgroup$ – Tim B II Jan 26 at 9:54
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    $\begingroup$ A variant of this is to hurl asteroids instead of nukes, at the right size and speed the blast and resulting winter will probably be similar but without the radiation. $\endgroup$ – lijat Jan 27 at 9:42

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