what lies beneath

despite Jules Verne, the g-field zeroes out
when at the center of a planet's sphere
as airless as the depths of space, no doubt
although the pressure's vastly greater there
but were it hollow, there's no up, no down
no bias to say how to orient
no force marks wall from ceiling, or from ground
the local space-time's perfectly unbent
our biosphere's a scant film on Earth's crust
the deepest-diving whale, and highest bat
can navigate in full implicit trust
that "up" is up, and 'X' and 'Y' lie flat
what anaerobes our core and mantle hold
I'll leave to fiction and to Thomas Gold