Earth’s history is divided into structured time units that geologists use to classify its geological and biological changes. These units, arranged from largest to smallest, help scientists analyze major events like mass extinctions, climate shifts, and evolutionary milestones.

• Eon: The broadest division, covering hundreds of millions to billions of years. Earth has four eons: Hadean, Archean, Proterozoic, and Phanerozoic.

• Era: Subdivisions of eons, spanning tens to hundreds of millions of years. The current Phanerozoic Eon contains three eras: Paleozoic, Mesozoic, and Cenozoic.

• Period: Smaller divisions within eras, marking distinct geological and biological changes. Examples include the Jurassic Period (Mesozoic Era) and the Quaternary Period (Cenozoic Era).

• Epoch: Periods are further divided into epochs, representing more refined time intervals. The Holocene Epoch is the current epoch, beginning roughly 11,700 years ago.

• Age: The smallest officially recognized division, representing more specific geological layers or climatic events.

Each of these divisions corresponds to significant transformations in Earth’s history, shaping both its landscape and the lifeforms that have evolved over time.