Geology

Geology is the scientific study of Earth - its materials, structures, processes, and history. To understand geology from first principles, we need to begin with its most basic building blocks.

At the most fundamental level, geology begins with atoms and elements. The Earth is primarily composed of eight elements that form its foundation: oxygen comprises 46.6% of Earth’s composition, followed by silicon at 27.7%, aluminum at 8.1%, iron at 5%, calcium at 3.6%, sodium at 2.8%, potassium at 2.6%, and magnesium at 2.1%. These elements combine through chemical bonds to form minerals.

Minerals serve as the building blocks of rocks, forming naturally occurring, inorganic solids with specific chemical compositions and crystalline structures. For instance, quartz forms when silicon and oxygen atoms arrange themselves in a specific geometric pattern. These minerals then combine in various ways to form rocks, which serve as the fundamental units of geological study.

The interaction of heat, pressure, and chemical processes creates three basic categories of rocks that continuously transform through the rock cycle. Igneous rocks form when magma cools and crystallizes into solid form. Sedimentary rocks develop when particles of other rocks or organic matter are deposited and compressed over time. Metamorphic rocks emerge when existing rocks undergo transformation through intense heat and pressure. This cycle directly influences Earth’s systems as rocks weather and erode in the atmosphere, transport through the hydrosphere, and eventually reform within the lithosphere.

These basic components interact through four major Earth systems. The lithosphere encompasses all solid rock formations. The hydrosphere contains all water on Earth. The atmosphere consists of the layers of gases surrounding our planet. The biosphere includes all living organisms and their interactions with the environment. The rock cycle demonstrates how these systems interconnect - for example, when oceanic plates in the lithosphere subduct beneath continental plates, they melt and form new igneous rocks, which may later be exposed to the atmosphere and hydrosphere through mountain building processes.

Two primary energy sources drive all geological processes on Earth. Internal heat, generated from radioactive decay and residual heat from Earth’s formation, powers processes like plate tectonics and volcanic activity. External energy from the Sun drives weather and climate patterns that shape the Earth’s surface.

Geological processes operate across vastly different time scales, ranging from immediate events like earthquakes to processes taking millions of years, such as mountain formation. This observation leads to one of geology’s most important principles: uniformitarianism, which states that present-day processes can help explain geological features formed in the past. For example, by studying how modern rivers create sedimentary deposits, geologists can interpret ancient river systems preserved in rock layers. Similarly, observing present-day volcanic eruptions helps us understand how igneous rocks formed millions of years ago, demonstrating how current processes illuminate Earth’s distant past.