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.
The Grave: שְׁא֣וֹל – sheol
The Dry Land
God made the dry land appear on the third day. The dry ground is, obviously, the surface of the Earth. For our purposes the surface of the Earth is considered to be a feature of the crust.
The Lower Parts of the Earth
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.