Because every piece of mass has its own gravitational field, the Earth&#x27;s total gravitational field is lumpy, not a smooth sphere. The lumps are caused by variations in the crust and mantle, like mountain ranges, valleys, and variations in rock types.<p>It is possible to map the lumps using a tool called a gravimeter, which is basically an extremely sensitive mass balance. This is one way in which we do observe (and use) tiny variations in gravity on Earth.