Our direct exploration of the interior of th eEarth by digging deep mines is limited by the fact that: Question 2 options: we soon encounter a completely fluid region that will not allow us to dig holes at all: it quickly fills in the Earth's self-gravity means that the enormous pressure causes any holes to collapse inward and fill in, even if the surrounding material is solid the rocks are far too hard to penetrate as we dig deeper, thanks to their very different composition the rocks are far too hard to penetrate as we dig deeper, thanks to the increased temperature they are under