- framework for 4.54 billion years of Earth history, divided into hierarchical units
- eons: Hadean, Archean, Proterozoic, Phanerozoic
- eras: Paleozoic, Mesozoic, Cenozoic (within Phanerozoic)
- periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary
- epochs: subdivisions of periods (Holocene, Pleistocene, Miocene)
- boundaries defined by extinction events, tectonic shifts, climate transitions
- radiometric dating (uranium-lead, potassium-argon, carbon-14) provides absolute ages
- deep time: the recognition that Earth’s age dwarfs human history by six orders of magnitude
- stratigraphy reads rock layers as a record of planetary entropy and renewal