One of the miners, Conway, reveals that the Daleks are planning to drop a bomb into their mineshaft to punch out the Earth's core, which will be replaced with a giant motor enabling the aliens to pilot Earth to their home world of Skaro.
The Daleks are planning to drop a bomb into their mineshaft to punch out the Earth's core. This is what one of the miners reveals. Conway is the miners. The Earth's core will be replaced with a giant motor. The Earth's core was enabling the aliens to pilot Earth to their home world of Skaro.