the seabed. This is nearly three times as deep as preceding oceanic drillings. A novel method of exploring the uppermost few hundred kilometres of the Earth was proposed in 2005, consisting of a small, dense, heat-generating probe which melts its way down through the crust and mantle while its position and progress are tracked by acoustic signals generated in the rocks. The probe consists of an outer sphere of tungsten about one metre in diameter with a cobalt-60 interior acting as a radioactive heat source. It was calculated that such a probe will reach the oceanic Moho in less than 6 months and attain minimum depths of well over in a few decades beneath both oceanic and continental lithosphere. Exploration can also be aided through computer simulations of the evolution of the mantle. In 2009, a supercomputer application provided new insight into the distribution of mineral deposits, especially isotopes of iron, from when the mantle developed 4.5 billion years ago. See also Internal structure of Earth References External links The Biggest Dig: Japan builds a ship to drill to the earth's mantle – Scientific American (September 2005) Information on the Mohole Project The Vredefort astrobleme, mantle plumes, core pipes, and tectonic-plate drift (www.impacttectonics.org) Structure of the Earth