Project Mohole

The project took its name from the Mohorovičić discontinuity, or Moho, the boundary between Earth's crust and mantle. Because oceanic crust is generally thinner than continental crust, project planners pursued drilling from a ship over the ocean. The goal was to recover mantle material directly, improving understanding of Earth's interior; reaching that boundary proved beyond the project's available means.

Project Mohole grew from discussions by the American Miscellaneous Society and received National Science Foundation funding in 1958. Its first phase tested whether deep-ocean drilling was technically possible. In March 1961, the converted drilling barge CUSS I operated off Guadalupe Island, Mexico, in about 3,800 metres of water. Thrusters and tracking equipment helped maintain the vessel's position over the hole, an early application of dynamic positioning. The drill recovered seafloor sediment and basalt, demonstrating the feasibility of drilling in deep water.

The project was conceived in phases, with experimental drilling preceding further vessel development and an eventual attempt to reach the Moho. Administrative disagreements and funding problems hindered continuation, and the program was cancelled in 1966 before its later phases and mantle objective were completed. Its practical lessons and demonstration of ship-based deep-ocean drilling helped support subsequent scientific drilling efforts. Project Mohole is therefore notable both for an ambitious goal it did not achieve and for advancing the tools and methods that made later ocean research possible.

Scientific ocean drilling developed into long-running international programs that recover sediment and rock cores and use borehole measurements to investigate seafloor history and Earth's structure. Project Mohole was an early precursor rather than the sole origin of this later work. It also showed how a difficult exploratory engineering project can yield lasting scientific capability even when the original objective remains unmet.