The basic oil derrick has an upright stationary section capable of supporting hundreds of tons of weight, combined with a movable boom used to raise and lower equipment. Derricks of various designs have been used for centuries to extract valuable resources from under the Earth. Early derricks consisted of a framework designed to hold a large pole for percussive drilling, accomplished by repeatedly beating the earth to make a hole. A modern oil derrick typically uses a drill bit capable of biting through the substrate and is cooled with a constant slurry of mud to prevent it from getting too hot.