How does scientists know earth has a solid core surrounded by mantle when we have never dug so deep? How do that happens when IMO 12 km is the deepest we have dug?

Question

How does scientists know earth has a solid core surrounded by mantle when we have never dug so deep? How do that happens when IMO 12 km is the deepest we have dug?

In: 1

Answer 1

We know that because we send sound waves down into the ground.

Sound waves move faster when they pass through solid material.

So measuring how those waves change as they move through the earth tells us what kind of material they have travelled through.