A word frequently translated as the grave is the Hebrew שְׁא֣וֹל – sheol, but sheol is far more than just the grave. The grave is a portal into the underworld realm of the dead.
Once you enter the great gulf nothing can stop your fall into the core. The pit is everything below the mantle. If the sides of the pit is the lower mantle, then the pit includes the great gulf.
You can scratch your head all day pondering the spiritual truth behind a supposed metaphor, or you can take it literally and deduce that the Earth above the waters refers to the crust and mantle.
The levels of hell aren't what you think. However, they're what we would expect. The Hebrews had a well developed idea of life after death. For them physical death, the grave, was a portal into a complex underworld realm: sheol.
The lower parts of the Earth, or nether parts, is one of several phrases which describe physical features of the interior of the Earth that we can assign to the mantle.
Here's a scary thought: if the beggar was carried by angels into Abraham's bosom, in a chamber in the lower mantle which overlooks hell, did other angels carry the rich man to the lip of the chamber and toss him into hell?
A common response to the human soul is that there isn't one because science can't detect it. However, we first detected gravitational waves in 2015. What else can't science detect? We don't know, science can't detect it.
Broadly speaking there are three contexts in which “foundation(s) of the Earth/world” are the scriptural basis for how we can understand three important concepts in our unified theory of everything.
We've found that the previous theory about the internal structure of Earth was induced, but no body knew any better so it was OK. We were in a state of blissful ignorance, assuming that ignorance was knowledge.
New research has uncovered a flaw in our understanding of the core — specifically, about the manner in which heat energy flows from the core and through the overlying mantle. The core is younger than the rest of the planet.