During this violent time, much of the debris would have resembled comets - dirty snowballs thought to be mostly slushy water surrounding a rocky core - slamming into Earth at velocities greater than 25 km per second (16 miles per second).

BBC: Comets could have seeded life on Earth

Balance is a crucial skill for surfers and one reason that many people who surf do exercises that strengthen the core in their out-of-water workouts.

WSJ: For the Love of Surfing and Wine Country

At Purdue University in Indiana, scientists are working on a reactor-like device that uses water circulated by gravity to keep the core cool.

CNN: Today/Tomorrow - Helping nuclear plants keep their cool

Mr Wolfowitz is not a banker, an economist, a public health specialist, a water management specialist, an agronomist, a climate change specialist - any of the professional specialisations that stand at the core of the poverty challenge.

BBC: NEWS | Americas | Head-to-Head: The right choice for the World Bank?