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
Bulletin of Engineering Geology and the Environment and groundwater conditions of geological formations; characterization of the mineralogical, physico-geomechanical, chemical and hydraulic properties of earth materials involved in construction, resource recovery and environmental change; assessment of the mechanical and hydrological behavior of soil and rock masses; prediction of changes to the above properties with time; determination of the parameters to be considered in analyzing the stability of engineering works and earth masses; maintenance of the environmental condition and properties of the terrain. Bulletin of Engineering Geology and the Environment The Bulletin of Engineering Geology and the Environment is a peer-reviewed scientific journal covering research in geoscience. It is