They study formation of ocean basins, pollution, earthquake activity, and petroleum and economic mineral potential. Engineering geologists determine suitable sites for the construction of roads, airfields, tunnels, dams, and other structures. They decide, for example, whether underground rocks will bear the weight of a building or whether a proposed structure may be safe in an earthquake-prone area. Mineralogists analyze and classify minerals and precious stones according to composition and structure. Geochemists study the chemical composition and changes in minerals and rocks to understand the distribution and migration of elements in Earth's crust.
Environmental geologists assess and remediate environmental sites or problems.
Hydrogeologists locate and characterize groundwater resevoirs and participate in the management and protection of this resource. Volcanologists study active and inactive volcanoes, lava flows, and other eruptive activity to try to predict their occurrence and minimize potential damage. Geomorphologists examine landforms and those forces, such as erosion and deposition, which cause them to change. Other geologists are primarily concerned with Earth history . Paleontologists study animal and plant fossils found in geological formations to trace the evolution and development of past life and to date sedimentary beds.