It forms at speeds of more than 1,000 mph (1,600 km/h), it lies deep beneath our feet, it could destroy hopes for alien life, and — finally — scientists understand how it works. Back in March, researchers writing in the journal Science revealed that they have found the first evidence for this ice, called "Ice VII." Scientists had predicted its existence beforehand. Under the right conditions, it was believed, ice could form in a pool of water without a layer of heat at the leading edge of its growing surface. That — along with super-intense pressures and temperatures — would...