Geology Cheat Sheet

The core ideas of Geology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Plate Tectonics

The theory that Earth's outer shell is divided into large rigid plates that move, collide, and separate on top of the semi-fluid asthenosphere. Plate interactions drive earthquakes, volcanism, mountain building, and the opening and closing of ocean basins over millions of years.

The Rock Cycle

The continuous process by which rocks are created, transformed, destroyed, and reformed through igneous, sedimentary, and metamorphic pathways. Energy from Earth's interior and the Sun drives this cycle, ensuring that no rock type is permanent.

Uniformitarianism

The foundational geological principle that the same natural laws and processes operating today have operated throughout Earth's history. Often summarized as 'the present is the key to the past,' it allows geologists to interpret ancient rocks by studying modern analogs.

Stratigraphy

The branch of geology concerned with the order, relative position, and age of layered sedimentary rocks. By applying principles such as superposition and lateral continuity, stratigraphy provides a framework for reconstructing Earth's chronological history.

Mineral Identification

The systematic process of classifying minerals based on physical and chemical properties such as hardness, luster, cleavage, crystal habit, color, streak, and specific gravity. Correct identification is fundamental to petrology, economic geology, and materials science.

Geologic Time Scale

The chronological framework that divides Earth's 4.6-billion-year history into hierarchical units including eons, eras, periods, and epochs. It is built from the fossil record, radiometric dating, and stratigraphic relationships, providing a common language for discussing deep time.

Volcanism

The processes by which molten rock (magma), gases, and ash are expelled from Earth's interior to its surface. Volcanism builds new crust, recycles materials, shapes landscapes, and can dramatically affect global climate through the injection of aerosols into the atmosphere.

Weathering and Erosion

Weathering is the in-place breakdown of rocks and minerals by physical, chemical, and biological agents, while erosion is the transportation of that weathered material by water, wind, ice, or gravity. Together they sculpt landscapes and produce the sediment that forms new sedimentary rocks.

Seismology

The study of earthquakes and the propagation of seismic waves through Earth's interior. Seismology has revealed Earth's layered internal structure and provides critical data for earthquake hazard assessment, early warning systems, and underground nuclear test detection.

Geological Mapping

The process of recording the distribution, nature, and age relationships of rock units, structural features, and surficial deposits on a map. Geological maps are essential tools for resource exploration, land-use planning, hazard assessment, and scientific research.

Key Terms at a Glance

Lithosphere:The rigid outer layer of Earth, comprising the crust and the uppermost part of the mantle, that is broken into tectonic plates.

Asthenosphere:The weak, ductile, partially molten layer of the upper mantle beneath the lithosphere, upon which tectonic plates float and move.

Mantle Convection:The slow circulation of material within Earth's mantle driven by internal heat, which is the primary mechanism driving plate tectonics.

Igneous Rock:Rock formed by the cooling and solidification of magma or lava. Intrusive igneous rocks cool slowly underground; extrusive igneous rocks cool quickly at the surface.

Sedimentary Rock:Rock formed from the accumulation and lithification of sediment (clastic), precipitation of minerals from solution (chemical), or accumulation of biological material (biochemical).

Metamorphic Rock:Rock that has been transformed from a pre-existing rock (protolith) by heat, pressure, or chemically active fluids without completely melting.

Magma:Molten rock located beneath Earth's surface, containing dissolved gases and crystals. When magma erupts onto the surface, it is called lava.

Tectonic Plates:Large, rigid segments of Earth's lithosphere that move, interact, and deform at their boundaries, producing seismic and volcanic activity.

Fault:A fracture or zone of fractures in Earth's crust along which there has been displacement of the two sides relative to one another.

Earthquake:A sudden release of energy in Earth's crust that creates seismic waves, typically caused by the movement of faults or volcanic activity.

Erosion:The process by which rock and soil are removed from one location and transported to another by natural agents such as water, wind, ice, and gravity.

Weathering:The in-place breakdown and alteration of rocks and minerals at or near Earth's surface by physical, chemical, and biological processes.

Stratigraphy:The branch of geology concerned with the study of rock layers (strata), their formation, composition, distribution, and the information they provide about geological history.

Fossil:Any preserved trace or remains of an organism that lived in the geological past, typically found in sedimentary rock.

Paleontology:The scientific study of life in the geological past through the examination of fossils, including the organisms' evolution, interactions, and environments.

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