Thanks. Useful information.

So since the mean depth of the Pacific's around 4000m, that means, without squishing them, we cannot even fit two layers. If we flip the top layer upside down, we should manage to match the tallest bits with lower bits, and fit them beneath sea level. ... since that top one's upside down now, and staying under sea level would be an arbitrary extra restriction I'd be imposing on myself, we can scrap that arbitrary restriction, and use that upturned flat cut underbelly to plonk a third ontop...

But that's still not as many stacked as I thought.

The pacific's tiny.

It can only hold about 1582 Polands.

The airspace above it belongs to a nation, so it's gotta be more

*clicks fingers and points*

Not deep enough.

Right.

Should have known.

Poles.

Tall.