We're all taught about the water cycle: that lovely diagram with the sun and the clouds and the rain and the rivers, all carrying water around in a nice loop. I'm happy to tell you that the diagram is still good sound science! However, lately we've learned about a second, tectonic water cycle that goes deep into the mantle. News stories have said there are great pools of water in the mantle that exceed the oceans! That is not good sound science. The water in the mantle is actually "water," and I can tell you more about both water cycles in my latest article, "The Earth's Two Water Cycles."