Crust (geology) crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth and so are not readily destroyed by subduction. Formation of new continental crust is linked to periods of intense orogeny; these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The crust forms in part by aggregation of island arcs including granite and metamorphic fold belts, and it is preserved in part by depletion of the underlying mantle to form buoyant lithospheric mantle. A theoretical protoplanet named
Alan (given name) is today Russia, and who were known to Classical writers in the 1st century CE. According to historian Bernard Bachrach, the Alans settled in parts of what is today France, including Brittany, in the Early Middle Ages. Bachrach stated that the use of forms of the name in given names, surnames, and place names, are evidence of the continued influence of the Alans on the Gaulish, Breton and Frankish peoples. The Breton name "Alan" can not be a direct loan from the ethnic name of the Alans (rendered as "Alānī" or "Halānī" in Latin, from Scytho-Sarmatian "*Al[l]ān-", derived from Old