Geology (from the Greek γῆ, gê, “earth” and λόγος, logos, “study”) is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates. In modern times, geology is commercially important for mineral and hydrocarbon exploration and for evaluating water resources; is publicly important for the prediction and understanding of natural hazards, the remediation of environmental problems, and for providing insights into past climate change; plays a role in geotechnical engineering; and is a major academic discipline. Geology is also a hobby for those who enjoy collecting various rocks, minerals and/or fossils.

Mineralogy

Petrology (from Greek: πέτρα, petra, rock; and λόγος, logos, knowledge) is the branch of geology that studies rocks, and the conditions in which rocks form.

Lithology was once approximately synonymous with petrography, but in current usage, lithology focuses on macroscopic hand-sample or outcrop-scale description of rocks, while petrography is the speciality that deals with microscopic details.

Sedimentology

Sedimentology encompasses the study of modern sediments such as sand, mud (silt), and clay,and the processes that result in their deposition. Sedimentologists apply their understanding of modern processes to interpret geologic history through observations of sedimentary rocks and sedimentary structures.

Sedimentary rocks cover most of the Earth’s surface, record much of the Earth’s history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.