the process by which rocks are constantly changing is called the rock cycle. it can take millions of years for rocks to change their form. the process includes melted rock that is sent to the earth's surface by volcanic activity. when it cools its forms igneous rock. next weather or rivers and another natural phenomenon will break the rock up into small pieces. over the years the sediments will build up and harden this will form sedimentary rock. through a slow process, sediment rock will get covered by other rocks resulting in them being transferred deep into the earth's crust. finally when pressure and heat get high enough sedimentary rock will transform into metamorphic rock and the rock cycle will start all over again.