Two billion years ago a meteorite 10km in diameter hit the earth about 100km southwest of Johannesburg, creating an enormous impact crater. This area, near Vredefort in the Free State, is now known as the Vredefort Dome... The meteorite, larger than Table Mountain, caused a thousand-megaton blast of energy. The impact would have vaporised about 70 cubic kilometres of rock - and may have increased the earth's oxygen levels to a degree that made the development of multicellular life possible... The original crater, now eroded away, was probably 250 to 300 kilometres in diameter. It was larger than the Sudbury...