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Leg 140 of the drilling ship JOIDES Resolution deepened Hole 504B in the eastern Pacific ocean by 378 m to a total depth of 2 km, making it the deepest penetration of the ocean crust (Figure 1). Contrary to previous expectations of much of the marine geology community, this demonstrated that deep crustal drilling can be performed in the oceans with currently available technology. Hole 504B is now believed to be at or within a few hundred meters of the critical boundary separating seismic layers 2 and 3, and reaching this boundary is an easily attainable goal. This, together with recent success in drilling lower crustal rocks in the Indian Ocean and the development of new strategies for deep crustal drilling, appears to open the way for the first systematic scientific investigation of the lower ocean crust and mantle through scientific ocean drilling.