Mountains that existed in Precambrian time were eroded into a subdued terrain terrain already during the late Mesoproterozoic, when the rapakivi granites intruded.[1] Further erosion made the terrain rather flat at the time of the deposition of Jotnian sediments.[2][3] With Proterozoic erosion amounting to tens of kilometers,[4] many of the Precambrian rocks seen today in Finland are the "roots" of ancient massifs.[5] The last major leveling event resulted in the formation of the Sub-Cambrian peneplain in late Neoproterozoic time.[6][7]