Earth's internal structure
Seismic waves generated by earthquakes travel through Earth's interior and bend or reflect at boundaries between materials of different density and composition, giving geologists a detailed picture of the planet's layered structure without ever drilling there.
Ice ages and glaciation
Earth has experienced at least five major glacial eras in its history, the most recent of which — the Quaternary ice age — began roughly 2.6 million years ago and technically continues today, with ice sheets still covering Antarctica and Greenland.
Mountain building and orogeny
Mountains form through orogeny — the deformation, thickening, and uplift of the crust at convergent plate boundaries, driven by subduction, continental collision, or the accretion of exotic terranes.
Plate tectonics
Plate tectonics is the unifying theory of geology, explaining earthquakes, volcanoes, mountain ranges, ocean basins, and the distribution of fossils as the surface expressions of a dozen rigid lithospheric plates in slow, continuous motion.
Radiometric dating methods
Radiometric dating measures the predictable decay of radioactive isotopes to determine the age of rocks and minerals, with independent methods consistently converging on the same dates.
Stratigraphy and sedimentary rock
Sedimentary rocks form in sequential layers called strata, and the principles that govern those layers — superposition, original horizontality, cross-cutting relationships — let geologists read Earth's history like pages in a book.
The geologic time scale
The geologic time scale is a hierarchical framework dividing Earth's 4.54-billion-year history into eons, eras, periods, epochs, and ages, each defined by characteristic rock sequences and fossil assemblages.
Volcanoes and igneous processes
Magma forms through three mechanisms—decompression melting, flux melting, and heat transfer—each associated with distinct tectonic settings such as mid-ocean ridges, subduction zones, and mantle hotspots.
What is Geology?
Geology is the scientific study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them.