There isn't actually a big bar magnet inside the earth. Instead, we think earth has a solid core made of iron and nickel, two magnetic materials.
Earth's magnetic field is produced in the earth's core, but the effect is the same as if there was a big bar magnet inside because all magnets and magnetic fields act in essentially the same way, regardless of their size or what produces them.
In your own words, describe one thing you learned or found interesting in this lab.