Could an ‘Ocean’ of Water Be Trapped Within the Earth?

Water covers 75 percent of the earth’s surface, but scientists are still trying to unravel its origin. One hypothesis suggests that crashing comets could have delivered the liquid, but some scientists say we should look under our feet rather than up towards the skies. Geophysicist Wendy Panero discusses how rocks deep within the earth’s mantle can trap water, and how this can enhance our understanding of the water cycle.