They locate rock layers cropping out on the surface of the ground in order to locate anticlines and domes. Geologists use data from existing wells to make subsurface maps of the reservoir rocks. By matching rock layers between wells, they can draw cross sections to find petroleum traps. Geologists study the physical aspects and history of the Earth. They identify and examine rocks, study information collected by remote sensing instruments in satellites, conduct geological surveys, construct field maps, analyze information collected through seismic studies, and use instruments to measure the earth's gravity and magnetic field.
Geologists study the composition, structure, and history of the earth's crust.
They try to find out how rocks were formed and what has happened to them since formation. There are numerous specialties falling under the two major disciplines of geology and geophysics. For example, petroleum geologists explore for oil and gas deposits by studying and mapping the subsurface of the ocean or land. They use sophisticated geophysical instrumentation, well log data, and computers to collect information. Paleontologists study fossils found in geological formations to trace the evolution of plant and animal life and the geologic history of the Earth.