Have you ever dug a hole in your backyard, or in the playground? How deep were you able to dig? One foot? Two feet? Or perhaps you really worked hard and were able to dig a hole that was three feet deep.
What would you need if you wanted to dig a really deep hole? You could use a shovel, but eventually it would become too difficult. As the hole became deeper, you would need a way to remove the dirt as you loosened it, otherwise you would not be able to throw the dirt out of the hole. As your hole became deeper, you would quickly dig through the soft regolith, or dirt, and begin hitting your shovel against hard bedrock. In order to continue digging, you would need a jack hammer or a drill to break through.Suppose that you had all of this equipment available to you, how deep could you dig? The deepest mines on Earth are only about 2.5 miles (4km) deep. Some geologists have used massive drilling equipment to take narrow core samples from as deep as 7 miles (11km) beneath the surface of the Earth.
This seems like a very deep hole, but when compared to the overall radius of the Earth, it is just scratching the surface. The Earth is approximately 4,000 miles (6,400 kilometers) from surface to center.