People who write about water like to say that the liquid in our drinking glasses and toilet bowls has been with us since the age of dinosaurs, continually recycled through plants, animals (including us) and the atmosphere. But really, some of the water on (and in) Earth was here billions of years before T. rex terrorized Triceratops. And now, research released today shows that, nearly 4.5 billion years ago, Earth shared some of that water with the Moon.