Scientists will set out this week to drill a hole into the Indian Ocean floor to try to get below the Earth's crust for the first time. They want to sample rock from the planet's mantle - its deep interior. In the process, the researchers hope to check their assumptions about the materials from which the crust itself is made. It will probably take several years to drop the full 5 to 5.5km, says co-team leader, Prof Chris MacLeod. Earth layersImage copyrightThinkstock Image caption The continental crust can be tens of km thick; the ocean crust is much thinner This is in addition to the 700m of water between the drilling ship, the Joides Resolution (JR), and the seabed.