At its centre, planet Earth is a ball of diamonds and precious metals, but all we can access are the few that are thrown to the surface. Scientists now believe there are a quadrillion tons (that's 1,000,000,000,000,000 tons) of diamonds out of reach far below the Earth's crust. They are at the same inaccessable depth where most of the planet's gold lies, around 160km deep when the deepest mine is only at 4. Any volunteers to start digging?