When the target is soft sediment that would be considerably altered by the rotation of the drill bit, water pressure is used to drive the hydraulic piston corer
developed by DSDP through the bit and into the sediment.
This technique's potential was first demonstrated, during DSDP's Leg 64 in 1970, when the prototype hydraulic piston corer
, brought aboard Glomar Challenger halfway through the cruise, performed spectacularly well in recovering laminated sediments in perfect condition at Site 480 in the Gulf of California.
The ice-rafted debris stratigraphy was reasonably dear in these regions, but use of the hydraulic piston corer
in the late 1970s along with improved resolution of the biostratigraphy, oxygen-isotope stratigraphy, and magnetic-reversal stratigraphy were needed before the timing of glacial onset could be determined precisely.