Chapter 2 - The Earth's crust

Abstract

This chapter reviews what is known about the physical and chemical properties of the crust, based on geophysics and chemically-analyzed samples. The Earth's crust is the upper rigid part of the lithosphere that is defined by a prominent seismic discontinuity, the Mohorovicic discontinuity or Moho. The chapter discusses the three crustal divisions—oceanic, transitional, and continental—of which oceanic crust and continental crust greatly dominate. The crust can be further subdivided into crustal types that are segments of the crust exhibiting similar geological and geophysical characteristics. The chapter lists the thirteen recognized crustal types in a table. The first two columns of the table summarize the area and volume abundances, and the third column describes tectonic stability in terms of earthquake and volcanic activity, and recent deformation. The chapter also discusses the average chemical composition of the upper continental crust, which is reasonably well-known from widespread sampling of Precambrian shields, geochemical studies of shales, and exposed crustal sections.