A device for extracting columns of sediment from the ocean floor. Deeper cores are taken by the piston corer, which can take samples as long as 20 meters. In a piston corer, a closely fitted piston attached to the end of the lowering cable is installed inside the coring tube. When the coring tube is driven into the ocean floor, friction exerts a downward pull on the core sample. The hydrostatic pressure on the ocean bottom, however, exerts an upward pressure on the core that will work against a vacuum being created between the piston and the top of the core. The piston, in effect, provides a suction that overcomes the frictional forces acting between the sediment sample and the inside of the coring tube. The hydraulic piston corer is used by deep-sea drilling ships and can take undisturbed cores of lengths up to 200 meters. Dates for the different layers are obtained by radiocarbon, paleomagnetism, or uranium series methods.