system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would it look like from the human perspective if the Earth was split down the middle and fell into two pieces?
gpt
Overall, gravity would keep the Earth together, as that is what it wants to do.  Unless some other force is going to actively push/pull them apart, generally, it'll just keep together.  Gravity for the most part.

However, the seam upon which the earth was split asunder would immediately start spewing lava, as the crust is no longer cohesive enough to contain the pressure of itself pressing on the lava, nor the heat pushing the lava out.

Volcanoes.  LOTS of volcanoes.  And plenty of immediate death and destruction.

But let's backtrack.  Something caused the split.  Whether it's a big beam, or a ginormous blade, or just *poof*, magic... that is going to cause local destruction as the blade/beam/? passes through the Earth.

Then earthquakes, on a scale that hasn't been seen in human history.  Massive amounts of now-destressed and restressed crust and mantle that are going to shift and push and pull and subduct and what not.  

And then the volcanoes.

It would go on long enough, and spew enough stuff into the atmosphere, that it's not the ground anyone would be worried about after about, oh, maybe 2 months or so... but the air.  It'd be causing a volcanic winter.  The Earth would grow colder due to the sun not getting through.  

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The second version is that there IS something that is going to push the Earth into it's two big halves.  Be interesting to see.  Some sort of forcefield, or just enough of a pressure wave to do it.  It is then turned off, and...

Ok, so... you have an edge where things are going to fall over.  Water from the oceans, and gigantic, amazing landslides, all over the edge, towards the center where the core's middle used to be.

You have this problem of the two halves still wanting to attract each other, but something started their journeys apart enough.  Fine.  Remember, the Earth is still spinning at a little over thousand miles an hour.  So what happens is that the core halves, both inner and outer, would get spun out of their center, and 'slosh' a little, as the uneven pressures and centripital or centrifugal forces cause some interesting results.  And yeah, they'll want to re-homogenize into one big lump of stuff, so they'd also start reaching for each other.

And so what happens to the mantle/crust shell is that it no longer has support.  The forces involved therefore start to rip the mantle/crust to shreds.  

Basically, at this point, you've just reset the Earth to the point where the moon formed, when the smaller planet bashed into what was Earth Mark I.  So now we're making Earth Mark II.  Only there'll be no new moon.

The various bits and pieces eventually reset and reform, including the oceans and continents and whatnot.  Whether life somehow finds its way back on board or not is going to be a question best left to someone else.

Depending on how far apart, the moon doesn't do anything, by the way, except 'watch' as it's gravimetric center doesn't change... so it just keeps orbiting the mess.  It might get hit by a stray rock or two from the resetting of the Earth, but that's about it.

Unless the halves are pushed really far apart, in which case, yeah, the moon can do some wacky orbits... and who knows?  Maybe even bash into the mess and make the earth even bigger than it is now.

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All in all, though.. it'd be bad.  Humans wouldn't like it.  At.  All.