Geology

Geology is the science that studies the solid Earth, the materials it is made of, and the processes that shape it over time. It examines rocks and minerals, the structure of the planet's interior, and the slow and sudden events — erosion, sedimentation, volcanism, earthquakes and mountain building — that continually reshape the surface and crust. As one of the geosciences, it overlaps with geophysics, geochemistry, palaeontology and Earth science more broadly.

A central framework in modern geology is the geological time scale, which divides Earth's roughly 4.5-billion-year history into eons, eras, periods and epochs. The long Precambrian interval is followed by the Palaeozoic periods — Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian — then the Mesozoic Triassic, Jurassic and Cretaceous, and finally the Cenozoic, whose epochs include the Eocene, Miocene and later divisions. Boundaries between these units are often defined by major changes in the fossil record, such as mass extinctions.

Geologists reconstruct the past using principles such as superposition, in which deeper rock layers are generally older than those above them, and by dating rocks with radiometric methods that measure the decay of unstable isotopes. Palaeogeographic maps, sometimes called palaeomaps, show how continents have drifted and how oceans have opened and closed across these long intervals. The findings underpin practical work in mineral and energy exploration, groundwater management, natural-hazard assessment and the study of climate change recorded in the rock record.

Frequently asked questions

What is the geological time scale?

It is a system that organises Earth's history into eons, eras, periods and epochs, with boundaries usually marked by major shifts in the fossil record or measured by radiometric dating.

What was the Precambrian?

The Precambrian is the long span before the Cambrian, covering most of Earth's history. Life was largely microbial, and well-preserved fossils of complex organisms are rare in its rocks.

How do geologists know the age of rocks?

They combine relative methods, such as the order of rock layers, with radiometric dating, which calculates age from the steady radioactive decay of certain isotopes in minerals.