From VOA Learning English, this is Science in the News.I'm Anna Matteo.And I'm Christopher Cruise.Scientists who study the Earth tell us the continents and ocean floors are always moving.This movement sometimes can be violent, causing death and destruction.Today, we examine what causes earthquakes and volcanic activity.The first pictures of Earth taken from space showed a solid ball covered by brown and green landmasses and blue-green oceans.It appeared as if the Earth had always looked that way -- and always would.Yet the surface of the Earth is not as solid or as permanent as had been thought.Scientists found that the surface of our planet is always in motion.Continents move about the Earth like huge ships at sea, floating on pieces of the Earth outer skin, or crust.New crust is created as melted rock pushes up from inside the planet.Old crust is destroyed as it moves toward the hot rock and melts.In the 20th century, scientists began to understand that the Earth is a great, living and moving structure.
