If you magically removed the mantle and core...

[Rye]

...what would happen? The crust and atmosphere are left behind, but the mantle and core have been teleported god knows where. How long would people survive? What would the effects be?

[Kuroneko]

So basically you're left with a ~25 km thick crust and hydrosphere, so you get about 0.6% of Earth's mass left, in a spherical shell. By Newton's law, gravity scales appropriately, and you lose the atmosphere pretty fast, since the escape velocity is now only slightly higher than the rms speed of air molecules.

I'm not sure how well the crust can keep together, but living in a microgravity environment with a rapidly depleting atmopshere makes that the least of one's worries anyway.

[Rye]

How long would the air last, minutes? What would the oceans do? Flash vaporise? Spread out into weird blobs? It's a mad idea I had for a short story, so yeah, perfunctory research is the aim of the game, here.

[Dave]

If the earth is still spinning at the same speed, won't the crust fly apart without any gravity to hold it down? I mean the centrifugal 'forces' would probably be more than the rock of the crust could take.

[D.Turtle]

Wouldn't the crust either collapse together or simply split into pieces and drift apart? After all, currently the Earth is being held together by its own gravity, with the crust "floating/sitting" on top of the mantle. It doesn't seem likely that the crust would stay in a single piece unmoving in its current position.

[LaCroix]

The crust isn't one piece. It's a couple of big pieces rubbing and pushing each other while they float along. Loosing gravitational pull to keep them on their (now non-existent) magma-lake means that they are instantly flung off and into each other. That will result in them getting shredded and turned into an asteroid field orbiting the sun.

[Feil]

It does what blobs of unattached matter do: the middle smears out, the top and bottom fall slowly towards one another. The atmosphere just goes 'fwish' and vanishes in very short order - there is, after all, an atmosphere of pressure trying to push it off the planet at all times, only restrained by gravity. Everybody dies within minutes, except a few people in sealed environments, who get enough time to figure out exactly how well and truly dead the human species is before they, too, die. The ISS gets a pretty cool show before they all starve and/or commit suicide and/or die of easily preventable accidents - they are, after all, completely safe, unless through some ridiculously unlikely bad luck they end up on a collision course with the moon.

As for the remaining bits: the moon drifts off and finds a new orbit, depending on which direction it was traveling when the cataclysm happened, trailing bits and pieces of us. The rest of us smears out eventually into an thin, insignificant asteroid belt, which the moon might eventually sweep clear.

At first I thought that dived submarines might do okay, but I'm pretty sure they'd just rupture from the sudden pressure change, since the only pressure in the water blobs would be surface tension.

[Pinjar]

It is just a guess but if we take Kuroneko's 0.6% of Earth's mass left as correct then if the crust is disturbed by the moon I would suggest that there should still be enough mass close enough together for the remains to form into a dwarf planet rather than an asteroid belt.

[LaCroix]

You dismiss the fact that the Moon is flung off by this, as well... Just like severing a cord that it spun on...

It will pull a part of the debris with it, but a lot of the remains will be scattered on a long 'tail' and form a belt.

In the next orbital periods, the moon might gather some of these fragments, but there is little hope that they will form a stable satellite body for the moon, rather than hitting it.

[Sriad]

The moon would stay on more-or-less Earth's orbit, but with a hunk more eccentricity. The moon's orbital speed WRT Earth is 1.0 km/h; Earth:Sun is 29.8. So at any time Luna's whizzing around the sun at 28.8-30.8km/s.

[Cykeisme]

Based on what has been said here, it's near-immediate dissociation of the remaining sub-1% mass due to lack of gravitational binding?
That sounds almost as devastating as Earth being hit by the Death Star.

[Feil]

Based on what has been said here, it's near-immediate dissociation of the remaining sub-1% mass due to lack of gravitational binding?

That is correct.