What has to happen when the domains in an object for it to become magnetic

When all or most of the domains are aligned in the same direction, the whole object becomes magnetized in that direction and becomes a magnet. The process of using a magnetic field to magnetize another object is called induction.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).