[outworlder]

On the other hand, imagine the neat tricks they could come up with using magnesium alone.

Would they have to be underwater, though? They could use the sea surface, provided the atmosphere is not toxic to them.

[civilian]

Yeah the sea surface is a glacier. There might be air pockets though? But it would also be near-freezing there, whereas the core would be much warmer, and would also have more pressure.

[36bydesign]

Isn't the surface frozen?