Rosa Lee Moses, age 14, of Timmonsville, South Carolina,  for her question:

How deep is the earth's core?

This zone in the interior of our planet is a mysterious one. Geophysicists have learned most of what they know about it by measuring the shock waves from earthquakes, some of which pass straight down through the globe. These shock waves vibrate at different frequencies as they pass through materials of different structure and density. They relay changing data as they pierce through deeper layers1nto the planet's interior.

Below the light rocks of the shallow crust there is the denser mantle. The material of this global shell forms a layer about 1,800 miles thick. It rests on the much denser and heavier material that forms the round core in the heart of the planet. The outer surface of this core is about 1,800 miles below ground level, plus the five to 20 mile thickness of the rocky crust. The denser core seems to have an outer layer about 1,400 miles thick and an inner ball about 1,600 miles in diameter.