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[WillowLuman]

Over two thousand?

How many would you need to put a noticeable crack into the Earth's crust?

Depends on where you detonate them. Those 2000 nukes were spaced out through the entire time Nukes have existed.

[Cryxis, Prince of Doom]

I'm sure if you detonated more than one in the Mariana Trench (or whatever it is called) you could make a decent crack

[MrWiggles]

I dont even think if you detonated the entire worlds arsenal of nukes at the bottom of the Mariana Trench it would breach to the mantel. You're talking huge numbers. Gigatonnes of force at work.

[WealthyRadish]

If you managed to nuke the moon enough to alter its orbit and have it crash into the Earth, that'd probably breach the crust. And prevent life from returning for a billion years. Maybe forever. Not sure how many nukes that would take, though.

[Zanzetkuken The Great]

Might be cheaper to use an asteroid that comes within near orbit.

[WealthyRadish]

I guess when you're trying to permanently destroy all life on the planet, doing so on a reasonable budget is important.

[Zanzetkuken The Great]

I guess when you're trying to permanently destroy all life on the planet, doing so on a reasonable budget is important.

I'm gonna Sig this when I get a good computer.

[Eric Blank]

Technically, one nuke would be plenty to put a crack in the Earth's crust. A really small one. The Earth just doesn't give a fuck about such a thing.

[Graknorke]

Was it America or Russia or multiple nations that detonated nukes in orbit to see what they would do?

Murrica
Operation Fishbowl

It's their plot to break through the glass ceiling that formed there after the biblical great flood.
INVERTED EARTH IS REAL MAN!

[martinuzz]

how many nukes would it take to create enough impulse to alter earth's orbit, I wonder

[Cryxis, Prince of Doom]

I think it would be more efficient to use the nukes for fuel in reactors powering gigantic engines if we were going to use them to move something

[Il Palazzo]

how many nukes would it take to create enough impulse to alter earth's orbit, I wonder

One. It's a matter of how noticeable you'd want it to be.

If you managed to nuke the moon enough to alter its orbit and have it crash into the Earth, that'd probably breach the crust. And prevent life from returning for a billion years. Maybe forever. Not sure how many nukes that would take, though.

Let's estimate it. To a good approximation, what we need to do is decelerate the Moon to zero orbital velocity. This involves bleeding off all of its kinetic energy in its current orbit, which takes about 7*10^28 Joules of work. Assuming an explosion on the surface can at best transfer half of its energy to the Moon, and taking an average nuke to have half a megaton yield, we'd need 7*10^13 nukes. That's over 14 billion times the number of nukes the US has got stockpiled.

Notice, it takes merely twice as much to blow up the Moon completely. We could go the extra mile.

[i2amroy]

I dont even think if you detonated the entire worlds arsenal of nukes at the bottom of the Mariana Trench it would breach to the mantel. You're talking huge numbers. Gigatonnes of force at work.

Yeah, basing my estimate off the Mariana Trench Explosion What-if XKCD figures I'd estimate you would probably be needing something like a million nukes before you even reached the "mass extinction" level, let alone the planet cracker level. (Though you would cause horrible hurricanes with even 1 nuke.

On moon nukes:
I'm not quite sure I agree with your numbers there. When I run the numbers I'm getting about 3.8*10^28 J for the kinetic energy, only about 2/3rds of what you are getting. Cut that down to the only 96% of the energy needed to cause a decaying orbit (as opposed to trying to stop it dead), and assuming half-megaton bombs as you did (which should release a total of 2.1*10^15 J each, assuming you somehow directed 100% of that into stopping the moon), I'm only getting a total of 1.737*10^13 bombs, about  1.7 billion times the amount the US currently has (and that's including a rough estimate of all nukes currently scheduled to be dismantled in the count).

Of course at that point if you wanted to destroy the world you could just glass the surface. A halfmegaton bomb gives us a fireball size of 882473 m^2 (thanks to this helpful site). Assuming we were able to channel the explosions into a better shape then circles, we could glass the entire surface of the planet (land and water) with only about 577 million bombs evenly spaced out. That's only like 24,000 times the worldwide total (once again estimating in decommissioned by not yet destroyed nukes).

Carrying this with some (very) rough estimates about yield, etc., I'm guessing the current nuclear stockpile plus retired weapons could probably glass about 1 ten millionth of a percent of the land area of the earth, or about 3030 square miles (about double the size of rhode island).

[WillowLuman]

I think it would be more efficient to use the nukes for fuel in reactors powering gigantic engines if we were going to use them to move something

http://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

[Il Palazzo]

@i2amroy:
KE doesn't match because I forgot to divide by two. 7 is a rounded number, and I think I was remarkably precise for a astronomy problem, as I hadn't rounded it up to 10.

With the effective yeld, you get twice as much because you assumed 100% efficiency, whereas(as stated in my post) I assumed only half is usable, as the other half goes directly into space upon detonation.