The Bible speaks about a foundation being laid for the earth. Don’t think of it as something at the core of the earth. It might be the heaven and the water canopy around this earth that provides it the stability.

In the beginning God created the heaven and the earth. – Gen 1:1.

Here is where we find God as the creator of time, space and matter, which means He existed before these came into being. He created the Heaven as His throne. He created the Earth simultaneously as His footstool. – Mat 5:34, 35. He sits in Heaven (the third heaven as we know it, from the Earth) and stands on the Earth. Definitely, He should have paid great attention to the place where His feet rest and stand. The earth is where God set His foot on! Here is where the Son of God set His foot on in His-story!

“Then the morning stars sang together, and all the sons of God shouted for joy”- Job 38:7.
Here is God asking man, “Where were you when I laid the foundations of the earth? Declare, if you have understanding. Who has laid the measures thereof, if you know? Or who hath stretched the line upon it? Whereupon are the foundations thereof fastened? Or who laid the corner stone thereof;”– Job 38:4-7.

God laid the foundations of the earth. We need not dig deep down the earth to discover its foundations as is our custom. The very heaven He created and the water that His Spirit was moving upon stood as a stabilizing structure for this earth to remain in its position though it would not have been ready for human habitation then. “He hath made the earth by His power, He hath established the world by His wisdom, and hath stretched out the heavens by his discretion.” – Jer 10:12. “God that made the world and all things therein” – Acts 17:24.