Structure of the Earth decay of radioactive elements, and freezing of the inner core. Structure of the Earth The internal structure of the Earth is layered in spherical shells: an outer silicate solid crust, a highly viscous asthenosphere and mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of
International Association for Engineering Geology and the Environment International Association for Engineering Geology and the Environment The International Association for Engineering Geology and the Environment (), formerly International Association for Engineering Geology, also known as IAEG (), is an international scientific society which was founded in 1964. It is affiliated with the International Union of Geological Sciences (IUGS) and has 3,798 members and 59 national groups all over the world. The association aims to promote and encourage the advancement of engineering geology through technological activities and research. At the same time it strives to improve teaching and training in engineering geology, and to collect, evaluate and disseminate the