Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
Geology of the Alps mountain ranges: the Apennines to the southwest, the Dinarides to the southeast and the Carpathians to the northeast. In the east the Alps are bounded by the Viennese Basin and the Pannonian Basin, where east–west stretching of the crust takes place. The Alps have a complex geology, but the general structure is the same as for other mountain ranges formed by continental collision. The Alps are often divided into Eastern, Central and Western Alps, even though the boundaries between these subdivisions are rather arbitrary. The division between the Eastern and Central Alps is approximately the line between St. Margrethen, Chur