<human>:  Why is the Earth’s crust so thick?
<bot>: The Earth’s crust is about 30 miles thick. The crust is thick because the Earth is a rocky planet, and rocky planets have thick crusts. The crust is made up of rocks and minerals, and the rocks and minerals are made up of atoms. The atoms are held together by forces called bonds. The bonds are made up of electrons, and the electrons are held together by forces called electromagnetic forces. The electromagnetic forces are the strongest forces in the universe, and they are responsible for holding the atoms together in the crust.