Worth knowing if you have a real pissy day.
From
http://ned.ucam.org/~sdh31/misc/destroy.html
Preamble
Destroying the Earth is harder than you may have been led to believe.
You've seen the action movies where the bad guy threatens to destroy the Earth. You've heard people on the news claiming that the next nuclear war or cutting down rainforests or persisting in releasing hideous quantities of pollution into the atmosphere threatens to end the world.
Fools.
The Earth was built to last. It is a 4,550,000,000-year-old, 5,973,600,000,000,000,000,000-tonne ball of iron. It has taken more devastating asteroid hits in its lifetime than you've had hot dinners, and lo, it still orbits merrily. So my first piece of advice to you, dear would-be Earth-destroyer, is: do NOT think this will be easy.
This is not a guide for wusses whose aim is merely to wipe out humanity. I (Sam Hughes) can in no way guarantee the complete extinction of the human race via any of these methods, real or imaginary. Humanity is wily and resourceful, and many of the methods outlined below will take many years to even become available, let alone implement, by which time mankind may well have spread to other planets; indeed, other star systems. If total human genocide is your ultimate goal, you are reading the wrong document. There are far more efficient ways of doing this, many which are available and feasible RIGHT NOW. Nor is this a guide for those wanting to annihilate everything from single-celled life upwards, render Earth uninhabitable or simply conquer it. These are trivial goals in comparison.
This is a guide for those who do not want the Earth to be there anymore.
Mission statement
For the purposes of what I hope to be a technically and scientifically accurate document, I will define our goal thus: by any means necessary, to render the Earth into a form in which it may no longer be considered a planet. Such forms include, but are most definitely not limited to: two or more planets; any number of smaller asteroids; a quantum singularity; a dust cloud.
Current Earth-destruction Status
Number of times the Earth has been destroyed: 0
Number of plans currently in progress with the final aim of bringing about the Earth's destruction: 0
Number of scientific experiments currently underway with the potential to bring about the Earth's destruction: 0
Minimum amount of time until the Earth is destroyed by natural means (discounting total existance failure): 25 years
Minimum amount of time until the Earth is destroyed by artificial means: 50 years
Know your enemy
Names: Earth, Terra, "the world"
Age: 4,550,000,000 years
Mass: 5,973,600,000,000,000,000,000 metric tonnes
Radius: 6,371 kilometres (average)
Surface gravity: 9.798 metres per second per second
Escape velocity: 11,186 metres per second
Physical structure (simplified):
Crust 0 to 35km Rock, hard and soft sediments, ice, miscellaneous 0 to 1000°C
Mantle 35 to 2900km Oxides of silicon, magnesium, iron and aluminium 1000 to 3700°C
Core 2900 to 6371km Iron (liquid, turning to solid at 5150km) 3700 to ~5000°C
Chemical composition by mass:
Iron 34.6%
Oxygen 29.5%
Silicon 15.2%
Magnesium 12.7%
Nickel 2.4%
miscellaneous 5.6%
Data from NASA and Wikipedia
Methods for destroying the Earth
To be listed here, a method must actually work. That is, according to current scientific understanding, it must be possible for the Earth to actually be destroyed by this method, however improbable or impractical it may be. This is a recent (2005|03|03) clarification of the rules intended to facilitate greater scientific accuracy. Up until now the rules were "I'll add it if I feel like it" and things were getting untidy. As a result of this change, several long-standing methods have been relegated to the "less scientifically probable" list.
Methods are ranked in order of feasibility.
Several methods involve moving the Earth a considerable distance off its usual orbital track. This is an essay in itself, so a separate page has been created for it.
Gobbled up by strangelets
You will need: Some strange matter.
Strange matter is a phase of matter which is even more dense than neutronium. (Wow.) It's theorized to form in particularly massive neutron stars when the pressure inside them becomes just too great for even neutronium to exist: the individual neutrons comprising the neutronium are instead broken down into strange quarks. The neutron star then becomes a "strange star" which is essentially a single gigantic nucleon.
Some theories suggest that a lump of strange matter ("strangelet") could remain stable outside of the intense pressure which created it. This would make it theoretically possible for strangelets of sizes all the way down to the atomic scale to exist. It's further theorized that the gravitational field of a microscopic strangelet would be enough to gobble up anything it comes in contact with, turning it into more strange matter.
Method: Hijack control of a particle accelerator. I suggest the Relativistic Heavy Ion Collider in Brookhaven National Laboratory, Long Island, New York. Use the RHIC to create a strangelet large enough to remain stable. Once created, your job is done: relax and wait as the strangelet plummets through to the Earth's core, where it will eventually swallow up the entire Earth.
Earth's final resting place: a huge glob of strange matter, of the order of a few kilometres across.
Feasibility rating (revised): 2/10. Evidence for the existence of strange matter is sketchy at best; there are a few neutron stars which look too small to be made of neutronium, there are a few earthquakes which might have been caused by a microscopic strangelet passing through the Earth at high speed, but that's about it. And even if it were possible that small stable strangelets could exist and swallow matter up in the manner described, the odds of forming one in a particle accelerator are pretty much zero.
Sucked into a microscopic black hole
You will need: a microscopic black hole.
Note that black holes are not eternal, they evaporate due to Hawking radiation. For your average black hole this takes an unimaginable amount of time, but for really small ones it could happen almost instantaneously, as evaporation time is dependent on mass. Therefore you microscopic black hole must have greater than a certain threshold mass, roughly equal to the mass of Mount Everest.
Creating a microscopic black hole is tricky, since one needs a reasonable amount of neutronium, but may possibly be achievable by jamming large numbers of atomic nuclei together until they stick. This is left as an exercise to the reader.
Method: simply place your black hole on the surface of the Earth and wait. Black holes are of such high density that they pass through ordinary matter like a stone through the air. The black hole will plummet through the ground, eating its way to the centre of the Earth and all the way through to the other side: then, it'll oscillate back, over and over like a matter-absorbing pendulum. Eventually it will come to rest at the core, having absorbed enough matter to slow it down. Then you just need to wait, while it sits and consumes matter until the whole Earth is gone.
Earth's final resting place: a singularity of almost zero size, which will then proceed to happily orbit the Sun as normal.
Feasibility rating: 2/10. Highly, highly unlikely. But not impossible.
Comments: Getting closer!
Source: The Dark Side Of The Sun, by Terry Pratchett. It is true that the microscopic black hole idea is an age-old science fiction mainstay which predates Pratchett by a long time, he was my original source for the idea, so that's what I'm putting.
Overspun
You will need: some means of accelerating the Earth's rotation.
Accelerating the Earth's rotation is a rather different matter from moving it. External interactions with asteroids might move the Earth but won't have a significant effect on how fast it spins. And certainly it won't spin the Earth fast enough. You need to build rockets or railguns at the Equator, all facing West.
Method: The theory is, if you spin the Earth fast enough, it'll fly apart as the bits at the Equator start moving fast enough to overcome gravity.
To do this the Earth will need to be spinning very fast indeed. Currently it rotates completely on its axis once every 24 hours. You'll need to spin it fast enough to perform a complete rotation once every 84 minutes.
Comments: This assumes that the Earth won't distort as it spins faster, which it will - the poles will flatten and the Equator will expand. It's also completely unknown what will happen once the rotation actually reaches the kind of speed we're looking at here. Will a ring of matter spontaneously lift off from the Equator and expand outwards? Will lumps of matter fly off at a tangent? If they do, will they come back down again? Will some other exchange of angular momentum occur to slow the planet down? The only thing we can be sure of is that Earth will not simply just fly apart into pieces. It'd take some computer modelling to find out what would actually happen.
Earth's final resting place: presumably, various lumps of matter expanding away from each other.
Feasibility rating: 3/10. Improbable, difficult, messy, and possibly not even workable.
Source: This method suggested by Matthew Wakeling.
Blown up by matter/antimatter reaction
You will need: 2,500,000,000,000 tonnes of antimatter
Antimatter - the most explosive substance possible - can be manufactured in small quantities using any large particle accelerator, but this will take some considerable time to produce the required amounts. If you can create the appropriate machinery, it may be possible - and much easier - simply to "flip" 2.5 trillion tonnes of matter through a fourth dimension, turning it all to antimatter at once.
Method: This method involves detonating a bomb so big that it blasts the Earth to pieces.
This, to say the least, requires a big bomb. All the explosives mankind has ever created, nuclear or non-, gathered together and detonated simultaneously, would make a significant crater and wreck the planet's ecosystem, but barely scratch the surface of the planet. There is evidence that in the past, asteroids have hit the Earth with the explosive yield of five billion Hiroshima bombs - and such evidence is difficult to find. It is, in short, insanely difficult to significantly alter the Earth's structure with explosives. This is not to mention the gravity problem. Just because you blasted the Earth apart doesn't mean you blasted it apart for good. If you don't blast it hard enough, the pieces will fall back together again under mutual gravitational attraction, and Earth, like the liquid metal Terminator, will reform from its shattered shards. You have to blow the Earth up hard enough to overcome that attraction.
How hard is that?
The gravitational binding energy of a planet of mass M and radius R is - if you do the lengthy calculations - given by the formula E=(3/5)GM2/R. For Earth, that works out to roughly 224,000,000,000,000,000,000,000,000,000,000 Joules. The Sun takes nearly a WEEK to output that much energy. Think about THAT.
To liberate that much energy requires the complete annihilation of around 2,500,000,000,000 tonnes of antimatter. That's assuming zero energy loss to heat and radiation, which is unlikely to be the case in reality: You'll probably need to up the dose by at least a factor of ten. Once you've generated your antimatter, probably in space, just launch it en masse towards Earth. The resulting release of energy (obeying Einstein's famous mass-energy equation, E=mc2) should be sufficient to split the Earth into a thousand pieces.
Greg Bear's novel, "The Forge Of God", contains an interesting refinement of this technique. Here, the antagonist instead generates antimatter in the form of a "slug" of anti-neutronium - superdense material massing a billion kilograms per cubic centimetre. This is fired into the Earth's core. Neutronium passes through ordinary matter as easily as a ball flies through the air, so the anti-neutronium slug doesn't annihilate immediately; rather, it builds up a protective sheath of plasma around it as it plunges downwards towards the Earth's core. It's then followed up by a slug of regular neutronium, which also falls into the core, at a time calculated to meet the first slug head-on at the exact centre of the Earth, where they annihilate themselves, and soon afterwards, the Earth itself. Highly space-efficient, and with the added bonus of all the energy being released at the Earth's core, where it can do the most damage. In the book, the antagonists simultaneously detonate nuclear warheads in certain oceanic trenches, to weaken the crust and allow the planet to be blown apart more easily.
Earth's final resting place: A second asteroid belt around the Sun.
Comments: trembling writes, "I still think that antimatter is crazy s**t, i.e. wouldn't want it on my flapjacks"
Feasibility rating: 5/10. Just about slightly possible.
Earliest feasible completion date: AD 2500. Of course, if it does prove possible to manufacture antimatter in the sufficiently large quantities you require - which is not necessarily the case - then smaller antimatter bombs will be around long before then.
Sucked into a giant black hole
You will need: a black hole, extremely powerful rocket engines, and, optionally, a large rocky planetary body. The nearest black hole to our planet is 1600 light years from Earth in the direction of Sagittarius, orbiting V4641.
Method: after locating your black hole, you need get it and the Earth together. This is likely to be the most time-consuming part of this plan. There are two methods, moving Earth or moving the black hole, though for best results you'd most likely move both at once. See the Guide to moving Earth for details on how to move the Earth. Several of the methods listed can be applied to the black hole too, though obviously not all of them, since it is impossible to physically touch the black hole, let along build rockets on it.
Earth's final resting place: part of the mass of the black hole.
Feasibility rating: 6/10. Very difficult, but definitely possible.
Earliest feasible completion date: I do not expect the necessary technology to be available until AD 3000, and add at least 800 years for travel time. (That's in an external observer's frame of reference and assuming you move both the Earth and the black hole at the same time.)
Sources: The Hitch Hiker's Guide To The Galaxy, by Douglas Adams; space.com.
Comments: It's clear that dropping the Earth into a singularity is massive overkill. A reasonably strong gravitational field, such as might be associated with any body between Jupiter and a neutron star, would be sufficient to rip the Earth apart via tidal forces. These possibilities are dealt with further down.
Meticulously and systematically deconstructed
You will need: a powerful mass driver, or ideally lots of them; ready access to roughly 224,000,000,000,000,000,000,000,000,000,000 Joules (see the antimatter method above for how this figure was arrived at).
Method: Basically, what we're going to do here is dig up the Earth, a big chunk at a time, and boost the whole lot of it into orbit. Yes. All six sextillion tonnes of it. A mass driver is a sort of oversized electromagnetic railgun, which was once proposed as a way of getting mined materials back from the Moon to Earth - basically, you just load it into the driver and fire it upwards in roughly the right direction. We'd use a particularly powerful model - big enough to hit escape velocity of 11 kilometres per second - and launch it all into the Sun or randomly into space.
We will ignore atmospheric considerations. Compared with the extra energy needed to overcome air friction, it would be a relatively trivial step to completely burn away the Earth's atmosphere before beginning the process.
Alternate methods for boosting the material into space include loading the extracted material into space shuttles or taking it up via space elevator. All these methods, however, require a - let me emphasize this - titanic quantity of energy to carry out. Building a Dyson sphere ain't gonna cut it here. (Note: Actually, it would. But if you have the technology to build a Dyson sphere, why are you reading this?) See later for a possible solution.
Earth's final resting place: Many tiny pieces, some dropped into the Sun, the remainder scattered across the rest of the Solar System.
Feasibility rating: 6/10. If we wanted to and were willing to devote resources to it, we could start this process RIGHT NOW. Indeed, what with all the gunk left in orbit, on the Moon and heading out into space, we already have done.
Earliest feasible completion date: Ah. Yes. At a billion tonnes of mass driven out of the Earth's gravity well per second: 189,000,000 years.
Source: this method arose when Joe Baldwin and I knocked our heads together by accident.
Pulverized by impact with blunt instrument
You will need: a big heavy rock, something with a bit of a swing to it... perhaps Mars
Method: Criminal, really, that this blindingly obvious method was overlooked for so long. Essentially, anything can be destroyed if you hit it hard enough. ANYTHING. The concept is simple: find a really, really big asteroid or planet, accelerate it up to some dazzling speed, and smash it into Earth, preferably head-on but whatever you can manage. The result: an absolutely spectacular collision, resulting hopefully in Earth (and, most likely, our "cue ball" too) being pulverized out of existence - smashed into any number of large pieces which if the collision is hard enough should have enough energy to overcome their mutual gravity and drift away forever, never to coagulate back into a planet again.
A brief analysis of the size of the object required can be found here. Falling at the minimal impact velocity of 11 kilometres per second and assuming zero energy loss to heat and other energy forms, the cue ball would have to have roughly 60% of the mass of the Earth. Mars, the next planet out, "weighs" in at about 11% of Earth's mass, while Venus, the next planet in and also the nearest to Earth, has about 81%. Assuming that we would fire our cue ball into Earth at much greater than 11km/s (I'm thinking more like 50km/s), either of these would make great possibilities.
Obviously a smaller rock would do the job, you just need to fire it faster. A 10,000,000,000,000-tonne asteroid at 90% of light speed would do just as well. See the Guide to moving Earth for useful information on manoeuvring big hunks of rock across interplanetary distances.
Earth's final resting place: a variety of roughly Moon-sized chunks of rock, scattered haphazardly across the greater Solar System.
Feasibility rating: 7/10. Pretty plausible.
Earliest feasible completion date: AD 2500, maybe?
Source: This method suggested by Andy Kirkpatrick
Comments: Earth is believed to have been hit by an object the size of Mars at some point in the distant past before its surface cooled. This titanic collision resulted in... the Moon. You can download a simulated video of the impact from this page. While the Mars-sized object in question obviously didn't hit Earth nearly as hard as we're proposing with this method, this does serve as a proof of concept.
Many useful planetary facts can be found here.
Frazzled by solar plasma
You will need: an extremely large, heat-insulated ring, lots and lots of wire, lots and lots of electricity
Method: Anybody who knows anything about the Sun, or has at least seen the opening titles of Star Trek: Voyager, knows that the Sun frequently erupts with huge rings of plasma called coronal rings and even huger rings of plasma called prominences. These, and sunspots, are caused by changing magnetic fields. Big prominences can break apart and cause coronal mass ejections, bursts of plasma which erupt into space and which can occasionally reach the Earth itself, where they can disrupt radio communications and cause blackouts.
Place your ring in as low an orbit over the Sun as you can manage. Now run an extremely powerful electrical current around the rim of the ring. High school physics will tell you that this will cause a powerful magnetic field passing through the middle of the ring. Carefully steered, you can use this ring to artificially induce a gigantic prominence and eject a much, much larger-than-average discharge of coronal plasma towards Earth. It'd probably be too much to expect just one carefully aimed CME to destroy the planet completely, but you can repeat the process over and over again, burning off layer after layer until the planet is gone.
Factors you will have to contend with include heat damage to your ring, targeting, and heat dissipation as the coronal plasma spreads out and crosses the gulf between the Sun and the Earth. You will want to fire as much plasma as you possibly can and focus it as tightly as you possibly can on the Earth. You could consider using other rings in higher orbits to focus the plasma after it's first ejected from the Sun, and further rings as relay stations en route. And these rings need to be BIG. Hundreds or thousands of kilometres across.
Earth's final resting place: Cooling lumps of matter, spread across the greater solar system.
Feasibility rating: 7/10. Excitingly plausible, though impossible with current space technology.
Earliest feasible completion date: AD 3000.
Source: This method suggested by "Thane".
Eaten by von Neumann machines
You will need: a single von Neumann machine, which subsists almost entirely on iron, magnesium, aluminium and silicon, the major elements found in Earth's mantle and core. A von Neumann machine is any device that is capable of creating an exact copy of itself given nothing but the necessary raw materials.
Theoretically, if it will be truly a von Neumann Machine, then its size doesn't matter: it can be any size from microscopic to planet-sized (though if you have the technology to take a body the size of the Moon apart and make a machine out of it, you have the technology to take the Earth apart and leave it in pieces), but it seems that miniature, molecular-scale nanobots, capable of building other nanobots and/or dedicated nanobot factories (nanoassemblers) would be the best way to go. It need not even be mechanical; all living things are technically biological von Neumann machines. Scott Lujan writes, "Through processes of directed evolution, perhaps beginning with diatomaceous microbes (capable of silicon processing) and choice natural subterranean extremophiles (can respire, i.e. oxidize, various heavy metals or live at extreme pressures and heats), one could conceivably create a strain of lithovores that would process earthly matter."
Method: Once you have your von Neumann machine built, release it into the ground under the Earth's crust and allow it to fend for itself. Watch and wait as it creates a second von Neumann machine, then they create two more, then they create four more. As the population of machines doubles repeatedly, the planet Earth will, terrifyingly soon, be entirely eaten up and turned into a swarm of potentially sextillions of machines.
Technically your objective would now be complete - no more Earth - but if you want to be thorough, then you can command your VNMs to hurl themselves, along with any remaining trace elements, into the Sun. This hurling would have to be achieved using rocket propulsion of some sort, so be sure to include this in your design. If you find yourself unable to design a VNM strong enough to stay intact at the core, you may need to do this in stages; consume a layer of the planet, launch into space, repeat.
Earth's final resting place: the bodies of the VNMs themselves, then a small lump of iron sinking into the Sun.
Feasibility rating: 8/10. So crazy it might just work.
Earliest feasible completion date: Potentially 2045-2050, or even earlier.
Source: 2010: Odyssey Two, by Arthur C. Clarke
Hurled into the Sun
You will need: Earthmoving equipment (note that the solar sail method listed here will not work for the obvious reason that the solar wind blows away from the Sun, and you want to go towards it).
Method: Hurl the Earth into the Sun, where it will be rapidly melted and then vaporized by the Sun's heat.
Sending Earth on a collision course with the Sun is not as easy as one might think; even though you don't actually have to literally hit the Sun (send the Earth near enough to the Sun (within the Roche limit), and tidal forces will tear it apart), it's surprisingly easy to end up with Earth in a loopy elliptical orbit which merely roasts it for four months in every eight. But careful planning can avoid this.
As far as energy changes are concerned, this method is inferior to the next one. The Earth is moving along its orbit at roughly 30km/s; to hurl it into the Sun, you'd need to counteract ALL of that, an energy change of a staggering 2,650,000,000,000,000,000,000,000,000,000,000 Joules. Read on...
Earth's final resting place: a small globule of vaporized iron sinking slowly into the heart of the Sun.
Feasibility rating: 9/10. Impossible at our current technological level, but will be possible one day, I'm certain. In the meantime, may happen by freak accident if something comes out of nowhere and randomly knocks Earth in precisely the right direction.
Earliest feasible completion date: Via act of God: 25 years' time. Any earlier and we'd have already spotted the asteroid in question. Via human intervention: given the current level of expansion of space technology, 2250 at best.
Source: Infinity Welcomes Careful Drivers, by Grant Naylor
Torn apart by Jupiter
You will need: Earthmoving equipment (solar sail method works fine here).
Method: Hurl the Earth into Jupiter, where it will be torn apart by tidal forces.
Moving the Earth out to Jupiter is much the same as moving the Earth in towards the Sun, the most obvious difference being your choice of vectors. However, there is another important consideration, and that is energy. It takes energy to raise or lower an object through a gravity field; it would take energy to propel the Earth into the Sun and it would take energy to propel it into Jupiter. When you do the calculations, Jupiter is actually rather preferable; while hurling the Earth into the Sun requires a 30km/s velocity change, hurling it out towards Jupiter requires a "mere" 24km/s of additional velocity, yielding an energy change of 1,670,000,000,000,000,000,000,000,000,000,000 Joules, or about 37% less than the figure given above.
Earth's final resting place: lumps of heavy elements, torn apart, sinking into the massive cloud layers of Jupiter, never to be seen again.
Feasibility rating: 9/10. As before, impossible at our current technological level, but will be possible one day, and in the meantime, may happen by freak accident if something comes out of nowhere and randomly knocks Earth in precisely the right direction.
Earliest feasible completion date: As before, via act of God: 25 years' time. Any earlier and we'd have already spotted the asteroid in question. Via human intervention: given the current level of expansion of space technology, 2250 at best.
Source: Mitchell Porter suggested this method.
Fall-back methods
If your best efforts fail, you needn't fret. Nothing lasts forever; the Earth is, ultimately, doomed, whatever you do. The following are ways the Earth could naturally come to an end. (They're no longer in feasibility order since it reads better this way.) Bear in mind that none of these will require any activity on your part to be successful.
Total existence failure
You will need: nothing
Method: No method. Simply sit back and twiddle your thumbs as, completely by chance, all 200,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 atoms making up the planet Earth suddenly, simultaneously and spontaneously cease to exist. Note: the odds against this actually ever occuring are considerably greater than a googolplex (1010100) to one. Failing this, some kind of arcane (read: scientifically laughable) probability-manipulation device may be employed.
Current feasibility rating: 0/10. Even if you look at the significantly greater probability of the Earth randomly rearranging itself into separate two planets, this is utter, utter rubbish.
Whipped by a cosmic string
You will need: a cosmic string and a whole lotta luck
Method: Cosmic strings are hypothetical 1-dimensional defects in spacetime, left over from earlier phases of the universe, somewhat like cracks in ice. They are potentially universe-spanning objects, thinner than a proton but with unimaginable density - one Earth mass per 1600m of length! All you need to do is get a cosmic string near Earth, and it'll be torn apart, shredded, and sucked in. Probably the entire rest of the solar system would be too.
Earth's final resting place: String.
Feasibility rating: 1/10. Mind-bogglingly unlikely. Even if cosmic strings do exist, which they may not, there are probably only about ten of them left in the ENTIRE UNIVERSE. And they can't be steered, unless you have godlike powers, in which case you might as well chuck into the Earth in the Sun and have done with it, so you're relying entirely on luck. This. Will. Never. Happen.
Source: this method suggested by Dan Winston.
Written off in the backlash from a stellar collision
You will need: another star. White dwarf is good, but we're not fussy.
Method: Crash your star into the Sun.
The interactions between the two stars in this very violent stellar event will cause more fusion to occur inside the Sun than normally does in 100,000,000 years. The result is not unlike a supernova explosion, though slower - a staggering amount of matter and energy is released outwards, burning the Earth to a crisp and firing it into interstellar space at best, completely incinerating it at worst.
Earth's final resting place: burnt pieces.
Feasibility rating: 4/10. This is listed under natural methods because there is absolutely no way you can move a star. Well, there are ways and means, but if you can move a star, why not move the Earth into that star? And the chances of this happening - even considering that in two billion years' time the Milky Way is going to collide with Andromeda - are very, very slim. Calculations suggest that the number of actual stellar collisions that are likely to occur in that exchange will be SIX. Six chances in about a hundred billion.
Hmm. That's actually pretty high for this list. Make it 5/10.
Source: This method suggested by Eric Thompson.
Swallowed up as the Sun enters red giant stage
You will need: patience
Method: Simply wait for roughly 5,000,000,000 years. During its natural progress along the Main Sequence, the Sun will exhaust its initial reserves of hydrogen fuel and expand into a red giant star - swallowing up Mercury, Venus, Earth and Mars in the process.
Earth's final resting place: Boiling red iron in the heart of the Sun.
Feasibility rating: 8/10. The problem here is that current scientific theories predict the Earth will probably survive. The increasing solar wind combined with the Sun's decreasing mass will result in the Earth gradually moving out to a wider, cooler, safer orbit.
Earliest feasible completion date: AD 5,000,000,000
Crunched
You will need: considerably more patience
Method: Our universe is rapidly expanding in all directions. It will likely continue to do so for a very, very long time. After that time, if the density of matter in the universe is greater than a certain critical value, the universe will slow to a stop due to mutual gravitational attraction, and collapse back together again, in a reversal of the Big Bang called the Big Crunch. Conditions during the Big Crunch will be similar to those during the Big Bang: mind-boggling heat, matter ripped to subatomic particles, fundamental forces such as gravitation and electromagnetism merging back together, that sort of thing. Yes, Earth would be destroyed. So would the rest of the universe. A tiny sphere of iron stands little chance against conditions like that.
Earth's final resting place: Quark-gluon plasma? Pure energy? Part of the next universe? Honestly, I don't know. But it won't be a planet anymore.
Feasibility rating: 8/10. Plausible. Assumes that the Big Crunch will actually occur at all, which is currently in question.
Earliest feasible completion date: AD 42,000,000,000, give or take
Source: Shields and Nick Snell both suggested this method.
Ripped asunder
You will need: about half as much patience
Method: Recent experimental results seem to show that the expansion of the universe is not slowing as one might imagine it would. In fact, the expansion is accelerating. It's a bit early to say with confidence why this is happening, though phrases like "dark matter" and "phantom energy" pop up pretty frequently, but anyway, it's conjectured that if the ratio w of dark energy pressure to dark energy density in the universe is negative enough (buh?), then the universe would expand, accelerating in its expansion until it was ripped apart at the seams. To quote Wikipedia's entry: "First the galaxies would be separated from each other, then gravity would be too weak to hold individual galaxies together. Approximately three months before the end, solar systems will be gravitationally unbound. In the last minutes, stars and planets will come apart, and atoms will be destroyed a fraction of a second before the end of time." Cool, eh?
Earth's final resting place: HAH! If I knew that, I wouldn't need aftershave.
Feasibility rating: 10/10. Likely. Assumes the Big Rip theory is correct, which it probably is, but might not be.
Earliest feasible completion date: AD 20,000,000,000, assuming w = -3/2 (could vary)
Source: a theory proposed by Robert R. Caldwell, Marc Kamionkowski, and Nevin N. Weinberg in February 2003. Read it here (PDF warning! Also, dense, difficult physics!). Brought to my attention by Jonah Safar and nanite.
Decayed
You will need: all-surpassing patience
Method: If the Big Crunch doesn't happen, and the Big Rip doesn't happen either, then we come back to the third option: the Big Chill. For this, the universe will just expand, forever. The laws of thermodynamics take over. Every galaxy becomes isolated from its neighbours. All the stars burn out. Everything gets colder until it's all the same temperature. And after that, nothing ever changes in the universe. For eternity.
A lot can happen in an eternity. Protons, for example, while incredibly stable, are believed to eventually decay like any other particle. So simply wait for a period of time of the order of 1,000,000,000,000,000,000,000,000,000,000,000,000 years, and roughly half of the constituent particles of Earth will have decayed into positrons and pions. If that's still too much like a planet for you, you could wait for another 1036 years, leaving only a quarter of the original Earth. Or wait even longer. Eventually there will be as little of Earth left as you wish.
Earth's final resting place: Miscellaneous positrons and gamma radiation (pions decay almost instantly into gamma ray photons) scattered thinly across the entire universe.
Comments: It's interesting to compare this method with the one right at the top (total existence failure). What we are essentially doing here is almost exactly the same thing, only instead of expecting every particle to disappear at once, we are waiting patiently for a significant proportion of them to disappear, one at a time, over the course of an unimaginable period of time. Essentially we've come full circle. The scientific theories involved are the same, it's just the time scale being considered which changes the feasibility rating from "astoundingly improbable" to:
Feasibility rating: 9/10. If all else fails, this one would be essentially unstoppable...
Earliest feasible completion date: AD 1,000,000,000,000,000,000,000,000,000,000,000,000
Source: This method suggested by Joseph Verock
Other, less scientifically probable ways that Earth could be destroyed
The following methods either
rely on scientific principles which do not currently (and may never) exist, or
have no discernable scientific justification.
For a method from fiction to be listed here, I've decided to draw a line and say that this method must have been used to destroy or threaten to destroy Earth or some similar planet. Simply having the potential doesn't count. For example, in the graphic novel Watchmen, Dr. Manhattan would probably have the capability to destroy the Earth... but nothing of the sort is ever hinted at in the book, so it's not listed here.
Existence negated via time travel
You will need: a time machine, heavy rock-moving equipment/explosives
Method: Using your time machine, travel back in time just over 4,500,000,000 years to shortly (i.e. a few billenia) before the formation of the Earth. What you should find in its place is a young Sun and an accretion disc formed of the dusty/rocky material that will later become our Solar System. Find the patch of material that is likely to condense into the Earth. Now blow up, split apart and otherwise stir up the material so that it never gets a chance to come together and form the Earth. Return forwards in time in several hundred-million-year jumps, repeating the process each time so that no planet of any kind ever forms at roughly 1 AU from the Sun. If you make an error, simply go back in time and try again.
If your time machine is more resilient, or you don't mind dying, you could consider going further back in time. The further you go, the less you need to change the universe to prevent the Earth ever forming. Go back to a few billionths of a second after the universe began and just by being there you'll completely alter the face of the universe to come... although it was pretty hot back then...
Earth's final resting place: When you finally return to the present day, you will be left with a largish asteroid belt where Earth should be. Alternatively, you may find that the matter has been assimilated into the bodies of other planets or the Sun.
Comments: Although originally placed in the first section, this entry was moved here - and stripped of its feasibility rating - because it relies on fictional technology and has no basis in real events or scientific theory. Time travel in this way is almost certainly impossible.
My good friend Rob rightly informs me that this course of action does not strictly speaking "destroy" the Earth - there is no actual destruction event in which the Earth goes from existing to not existing. What one ends up with instead is a universe in which the Earth does not and never did exist.
Destroying Rob proved remarkably easy.
Engulfed in supernova
You will need: Some means of inhibiting nuclear fusion reactions.
Method: Simply cause the Sun to suddenly halt all its nuclear fusion reactions, thereby collapsing and then exploding with enough energy to momentarily outshine the entire rest of the galaxy. This one's actually pretty tricky, since as yet there is no scientific theory which could allow you to induce the Sun to go supernova. However, it does promise to be one of the most efficient and spectacular ways to destroy the Earth, so if you have the necessary skills and machinery, then I would recommend this over most other methods.
Earth's final resting place: a smear of vaporized iron moving across the universe at roughly 5% of the speed of light.
Comments: Although originally placed in the first section, this entry was moved here - and stripped of its feasibility rating - because it relies wholly on fictional technology and has no basis in real events or scientific theory.
Source: The Songs Of Distant Earth, by Arthur C. Clarke
Reduced to subatomic dust
You will need: a strong nuclear force destabilizer
SNFDs are completely outside the range of modern science, but the method sounds vaguely plausible, so here it is. The strong nuclear force is what holds atomic nuclei together and, for example, stops people from flying apart into clouds of free quarks. Simply aim your SNFD at Earth and fire, or activate it while on the ground, or however your model works (design may vary). Congratulations. The Earth is now an expanding cloud of dust.
Earth's final resting place: a cloud of randomized subatomic matter.
Comments: Although originally placed in the first section, this entry was moved here - and stripped of its feasibility rating - because it relies wholly on fictional technology and has no basis in real events or scientific theory.
Source: N64 game Perfect Dark, by Rareware
Induced to go nova/collapse into a black hole via injection of a Neutronium Alchemist - Night's Dawn Trilogy
From the Hitchhiker's Guide To The Galaxy universe:
Demolished by a Vogon Constructor Fleet
Disappeared along with the rest of the universe and replaced with something even more bizarrely inexplicable due to somebody discovering exactly what the universe is for and why it is here (note that this is only a theory, even in the Guide universe)
Silenced by a well-placed pulse from the Death Star - Star Wars. An extremely in-depth discussion of the Death Star superlaser which incidentally includes some discussion of the order of magnitude of energy required to destroy an Earthlike planet can be found here.
From the Marvel universe, destroyed by any of:
Galactus
The Beyonder
Molecule Man
Any unscrupulous individual with a Cosmic Cube
The Living Tribunal
Eternity
Thanos, or anybody else with the Infinity Gauntlet
Dark Phoenix
Captain Marvel III
Any Celestial
The Infinites
Surter
The Ultimate Nullifier
From the DC universe, destroyed by any of:
The Anti-Monitor
Darkseid
Mageddon
Solaris
The Spectre
Eaten by Unicron
From the Star Trek universe:
Swallowed by the Doomsday Machine
Destroyed by the Xindi
Imploded after some Martians remove a portion of the planet's core, leaving void - Stranger In A Strange Land, by Robert Heinlein
Something something evil Willow something something black magic something - Buffy The Vampire Slayer
Nullified by AKKA - Legion Of Space, by Jack Williamson
From the Dragonball/Dragonball Z/Dragonball GT universe:
Blown up by a massive ki blast (either instantly, or after five minutes/six episodes' ominous rumblings)
Destroyed by unknown means for unexplained reasons because nobody got all the Black Star Dragonballs back together
From the Marathon universe:
Blown up by an early nova induced in the Sun by the trih xeem
Dissolved along with the rest of the universe and time itself after the release of the W'rcacnter
From the Lexx universe:
Eaten by the Lexx
Destroyed along with the rest of the universe by Gigashadow
From the Babylon 5 universe:
Blasted by a Vorlon Planet Killer beam
Shadow missile drills (?)
Open a few jump points inside the Sun, draining it of mass, causing it to go nova
Drain the Atlantic ocean into the Earth's core, setting off an explosion of superheated water vapour - Doctor Who
Explosively space-modulated by an Illudium Q-36 Explosive Space Modulator - Marvin the Martian
Nova-bombed by a Nova Bomb - Andromeda
Ripped apart by tendrils of black energy from a "Death Reborn Revolution" super-senshi attack - Sailor Moon
Blasted out of existence by Ideon, the most ridiculously overpowered mech in animated history - Space Runaway Ideon
ambradley writes, "It seems you've neglected the method in the movie 'Supernova' with James Spader and Lou Dimond Phillips, in which a bomb containing 9th dimension material was detonated near a supernova. Due to the property of 9th dimension material, the onboard computer explained that the explosion would continue until all 3rd dimension matter in the universe was expended. That would get a bit more than the Earth, but it would be destroyed along with everything else..." Thanks for that great bit of non-science, ambradley!
Destroyed by God. Far be it from me to dictate whether God does or does not exist, but if he did, and was omnipotent, then no doubt he could destroy the Earth at a mere thought if he should decide to. Of course, the question arises of how we persuade him to do this.
One suggestion - should Judaic mythology turn out to be correct - is finding and killing one or more of the Lamed Vav Tzadikim, 36 righteous men whose role in life is to justify the purpose of mankind in the eyes of God. If even one of these is missing, it is said the world would come to an end. Practically speaking, it would probably be easier to wipe out humanity than to find one these individuals, who do not themselves know who they are.
Mike Trainor writes, "Just because we don't have the technology to destroy the planet doesn't mean no one else in the universe does. What you need to do is to point our most powerful radio-telescope transmitters at likely solar systems and taunt them. 'The girly-beings in your miserable solar system could never destroy a planet as cool as this one...'" Thanks, Mike. We'll get SETI on it.
Things which will NOT destroy the Earth
Gamma Ray Burst'd
You will need: a star in Earth's stellar neighbourhood with >40 solar masses. Such massive stars are hard to come by; even Betelgeuse has only 20 solar masses. The best candidate I know of is Eta Carinae, which has over 120 solar masses but is ~7500 light years away.
Method: Gamma ray bursts are powerful, short-lived floods of gamma ray photons. GRBs come in two flavours, short (less than 2 seconds) and long (2 seconds to about 3 minutes); the latter are believed to be caused by stellar explosions called hypernovae, hundreds of times more violent than ordinary supernovae. Such stars are usually billions of light years away when they explode - the fact that we can detect them at this range should tell you enough about how powerful a hypernova is. So how about triggering one locally? Any such explosion within about 20 light years would probably be violent enough to destroy the Earth itself.
Feasibility rating: 0/10. This method was originally listed above, but astronomer Stephen Thorsett set me straight. It wouldn't work. Even in the titanic quantities described above, gamma rays wouldn't make a dent in Earth's actual, physical structure.
Sources: Lycurgus suggested this method. Further information from nasa.gov.
Burned away by muon-catalyzed fusion of the oceans
You will need: a supply of muons
Method: The theory runs like this. A muon is a negatively-charged particle somewhat like an electron. If you dump a load of muons into some hydrogen, then some of the muons will replace the electrons in the hydrogen atoms. Because of the mass difference, the hydrogen atoms will suddenly get much smaller, causing the hydrogen molecules to be much closer together; enough that the probability of the hydrogen nuclei just randomly fusing with each other is high.
So, if you instead poured your muons into the oceans, they could cause the deuterium chemically combined with the water in the oceans to spontaneously begin undergoing fusion reactions. In theory, the amount of heat/energy released by the fusion of all the water in the world would be enough to destroy it by a good few orders of magnitude.
Feasibility rating: 0/10. All known muons we know about decay in a few microseconds - fairly long for an exotic subatomic particle, but still too short to be practical, so unless you can generate your muons in bulk, for free, you don't reach energy break-even, and the fusion stops as soon as it starts instead of being self-sustaining.
Sources: Muon-catalyzed fusion was theorized in the late 1940s by Andrei Sakharov, and brought to my attention by Jef Poskanzer
Comments: This method was never listed as plausible, but I put it up here anyway because the idea itself is intriguing, even if it wouldn't work.
Blown up by vacuum energy detonation
You will need: some means of extracting energy from the vacuum
Method: Some scientific theories tell us that what we may see as vacuum is only vacuum on average, and actually thriving with vast amounts of particles and antiparticles constantly appearing and then annihilating each other. It also suggests that the volume of space enclosed by a light bulb contains enough vacuum energy to boil every ocean in the world. Therefore, vacuum energy could prove to be the most abundant energy source of any kind. Which is where you come in. All you need to do is figure out how to extract this energy and harness it in some kind of power plant - this can easily be done without arousing too much suspicion - then surreptitiously allow the reaction to run out of control. The resulting release of energy would easily be enough to annihilate all of planet Earth and probably the Sun too.
Earth's final resting place: a rapidly expanding cloud of particles of varying size.
Feasibility rating: 0/10. This method was originally listed as plausible, but Alan Thomas set me straight: there are about five different ways to calculate the energy of the vacuum, all giving different answers. The methods which give the answers "large" or "infinite" are predicated on dodgy mathematics and almost certainly wrong.
Source: 3001: The Final Odyssey by Arthur C. Clarke
Armageddon, as described in the Bible. Armageddon does not destroy the Earth, nor even everyone on it. One third of the human population is wiped out repeatedly (at least one third and then another third of what's left) but then not only does the remnant survive, but God's people return from heaven and get to live in a city roughly the size of Brazil. This is as far from our definition of destroying the Earth as you can reasonably get, as the planet is still there AND people still live on it.
Paradoxes as described in Back To The Future Part II. By definition, a paradox cannot actually come into existence.
Ceasing all thought (if the Earth is not observed, then how can it exist?). Philip K. Dick said it best: "Reality is that which, when you stop believing in it, doesn't go away."
Semantics. A few people suggested exploiting a loophole in my mission statement and moving the Earth into orbit around a gas giant, making it a moon rather than a planet. Yeah, yeah, very good. Get back to work.
Detonating all the nuclear weapons ever created simultaneously, either all at one location or strategically placed around the globe. This will irradiate pretty much the entire globe and kill an awful lot of people, animals and plants, but will actually destroy very little of the planet itself.
Proving that 1=0. If one did indeed equal zero, so it is reasoned, then since there is one Earth, there must be zero Earths... so, if one could prove it, the Earth would cease to exist. This is specious logic. Finding a proof in mathematics does not magically change a fact from being false to being true. It merely verifies rigorously as true a fact that always was true. Thus, if 1=0 could be proved, then it would always have been true and the Earth should never have existed. But Earth is still here. QED.
Runaway fission at the Earth's core, as proposed by Tom Chalko. It is true that while the Earth is mainly iron, there are significant quantities of other trace elements present, including fissile materials like uranium, thorium and - get this - radioactive potassium which have sunk to the core where latest studies suggest where they are indeed undergoing fission, generating heat and keeping the interior of the Earth warm. However, if a nuclear explosion did occur at the core, it would be insulated from the surface by sixty-three hundred kilometres of liquid iron.
Gay marriage.
General mundicide strategy
Destroying the Earth is not as easy as pressing a big red button. It takes decades of hard work.
Planning
Without a plan, you have nothing. Sooner or later you WILL hit a snag and find yourself unable to continue: government agents will start lasering their way through your door, or you'll have your superweapon ready and armed but nowhere safe to stand when you fire it, or you'll just plain run out of money. You need to plan for as many eventualities as you can conceive of, as early as possible. When I say early, I mean early: ideally your plan should be at least 50% complete by the time you leave high school, because your career choices will be a very significant factor. You should have picked your method by this time too. (The list above isn't necessarily complete - if you come up with a better way of your own, good luck to you.) Once you have picked your method, STICK TO IT.
Assuming, of course, that you and whatever trusted advisors you will allow to side with you do not intend to "go down with the ship", it is particularly advisable to make plans for alternate living arrangements before you embark on a course of action which may result in the destruction of the Earth. Since in most cases the hypertechnology required to actually destroy the Earth is ridiculously advanced, access to an interstellar spacecraft, a space station or another habitable planet is likely to be well within your grasp, but this is not something you want to start making assumptions about.
Careers
At this point you need to make a very significant decision: are you going to design your doomsday machinery (all of the above methods except Total Existence Failure require a greater or lesser amount of machinery) yourself, or are you going to employ somebody else to do it for you? Unless you are an extremely gifted scientist and you really can destroy the Earth from your laboratory (which is not impossible; see the Strangelet or Von Neumann Machine methods), you're fairly likely to pick the latter.
If you do decide to design (and possibly build) this thing yourself, you'd be advised to pursue mainly sciences, with the main emphasis on physics (quantum, atomic, and astrophysics in particular), but also some electronic and mechanical engineering, mathematics and possibly robotics. After this, get a job working with the technology you hope to harness, build your doomsday machine in your lab, and bam, you're done.
If you don't decide to design your doomsday device yourself, and from here on, I'll assume that this is what you decided, then the plan becomes rather more complicated and your career choices will be very different. Your time in secondary and higher education would probably be best invested studying finance, economics and politics, brushing up your management, speaking and people skills, honing your powers of persuasion, and learning to exude charisma. Charisma is a big one. These skills will enable you to hopefully ascend to a position where you have access to three things:
money,
resources and
manpower.
If this is a lab project as described above then you'll need relatively little of all of these; enough money to run a lab, resources to keep it stocked, and manpower in the form of one or more brilliant scientists to (knowingly or otherwise) construct your doomsday device. That suggests that the best place to seek employment would be at a research institution for the areas of science you hope to employ, or maybe an organization like Boeing or NASA... failing that, found the organization yourself!
If this is a big, possibly space-based project then you will need MUCH more to work with. You need to either work in politics or the armed forces. Politics would be an excellent choice. I say without cynicism that today, of all the people in the world, the President of the United States of America would be the person most likely to be able to destroy the Earth should he decide to. If you feel you lack the ability to make it in politics (knowledge of your weaknesses is a strength), you should join the armed forces and shoot for Supreme General or whatever the highest rank is.
Nancy Lebovitz suggested religion as an alternate means of gaining resources, money and manpower. Religion is undeniably a very powerful force. If you could set yourself up as a religious leader you could potentially gain a lot of supporters - who would be much more dedicated to you as a leader than a soldier would be to his general or a citizen to his King/President/Supreme Dictator-For-Life. Setting oneself up as a new prophet doesn't seem to attract much more than scepticism in this day and age, so unless you were very persuasive, you'd probably experience greatest success by hijacking an existing mainstream religion for your own ends. One potential pitfall is that there's a limit to what your followers can provide you in terms of monetary offerings and labour. Manpower alone is not enough. You'd still need at least one scientific mastermind, and frankly I see scientific masterminds as being among the least likely to follow you... But this is a kink you should be able to work out.
Of course, by the time it becomes even possible to destroy the Earth, Madagascar might be the dominant superpower, or the whole world might be unified as a single nation, or maybe the whole galaxy is full of humans, there's no such thing as money, and solid platinum asteroids and robot workers are plentiful. I don't know. Whatever you can manage. Anyway, once you have everything you need at your disposal, make the calls, submit your proposals, and set the project in motion.
Your base
At this point you will probably need to set up some sort of base of operations. It should be at a safe distance from Earth. Lurking at least one AU out of range of whatever terrible destructive force you are about to unleash is strongly recommended in most cases, but for the supernova particularly you'll want to put as much as a thousand light years between yourself and the Earth when it happens. If you have to be physically on Earth to begin the destruction process (e.g. hurled into Sun, antimatter blast), then set a countdown. Make sure the countdown timer is a) thoroughly tested and b) tamper-proof. The same goes for your escape route offplanet.
If you are currently Supreme Dictator of Earth, you could simply announce your intentions directly to your enslaved populace with relative impunity. If you can come up with some really, really good reason for destroying the Earth which people will actually agree with - for example, you want to build a far more spacious Banksian Orbital (or many of them) instead - then getting humanity on your side will prove incalculably useful. However, as a rule, you should try to keep the true purpose of your project secret from as many people as possible for as long as possible. Some methods are much easier to cover up than others, and this should have been a major factor in your initial choice of method. If absolutely nobody apart from you knows the true purpose of your supernova-inducer until two hours after it becomes too late to turn it off, so much the better. Despite this, you should plan for (and construct your base in preparation for) your project to ultimately become public. This could occur at any time, you might have months, hours or seconds to go. This is actually the biggest potential stumbling block, and a situation you'll have to prepare for very, very carefully. Depending on how much time your opponents have to act, how powerful they are, and whether you know they know or not, they might make anything from a very desperate move (launching nukes at your space station regardless of the thousand innocent hostages on board) to a very subtle one (invisibly manipulating you into employing one of their undercover agents in your laboratory security forces). Your base will therefore need very strict security procedures, many layers of defence, and multiple redundancy and carefully programmed emergency overrides for every system, critical or not. You'll need weapons. And doors. Heavy doors. Assuming the worst, you personally should always be armed. If your base is in space you should permanently be wearing your space suit under your clothes. In case of betrayal, you should be able to run the entire show single-handedly from your locked-down control room, from which you should of course have an escape route.
You should always, always, always have an escape route.
See also The Evil Overlord list for lots more general advice on building bases, planning escape routes, handling enemy incursions, and other tangentially related topics.
Finally
If the method you choose can be tried more than once (e.g. hurled into Sun, vacuum energy detonation), and your budget will stretch, you could consider practicing on smaller astronomical bodies and working your way up. For example, consider destroying Mercury, or Ceres. Don't forget to take notes on what went particularly well, what didn't work, what was unnecessary, etc., just so everything goes as smoothly as possible on the big day.
Take a camera. Most of the methods listed above are incredibly spectacular and witnessing them will probably be once-in-a-lifetime opportunity for you, so remember to capture the moment.
And lastly, if all your efforts fail, don't give up! Remember, nobody has ever successfully destroyed the Earth.
eter, aka 
usty 
halk
