Every day, ore and minerals taken from deep under the Earth's crust are used to make steel, cement, glass, and other products. Workers in mining operations employ tools and equipment to extract these resources in frequently difficult and potentially hazardous situations. Continuous mining machines are self-propelled behemoths that rip coal, ores, rock, or sand from mine faces and deposit it on conveyors or shuttle cars. Mine cutting and channelling machines extract materials from the Earth's surface by cutting or channelling along the face or seams of coal mines and stone quarries. Operators ensure that these machines work smoothly and safely, and that mining facilities are stable and ventilated. Adjustments are made to maximise machine operations, and equipment is repaired as needed. Earth drillers utilise a variety of drills to extract water and salt deposits beneath the Earth's surface, to take core samples during mineral exploration or soil testing, and to make explosives more effective in mining or building. Earth drillers and mine cutting machine operators often require a high school diploma, although continuous mining machine operator employment typically do not require any specific qualifications.