Erathem

An erathem is a major division of geologic time, representing the largest subdivision of the Phanerozoic Eonothem (the visible life eonothem). Erathems correspond to a significant stage in the history of life on Earth, characterized by relatively distinct assemblages of fossils.

Erathems are subdivided into systems (periods), which are further divided into series (epochs), and finally into stages (ages). The Phanerozoic Erathem is divided into three erathems:

• Paleozoic Erathem: "Ancient life," spanning from the Cambrian explosion to the end-Permian extinction.
• Mesozoic Erathem: "Middle life," often called the Age of Reptiles, characterized by the dominance of dinosaurs.
• Cenozoic Erathem: "Recent life," the current erathem, characterized by the rise of mammals and flowering plants.

The boundaries between erathems are typically defined by major extinction events or significant changes in the fossil record. The term "erathem" is used when referring to the rock strata laid down during a particular era, while "era" is used to refer to the corresponding time period. For example, the Mesozoic Era is the time period, and the Mesozoic Erathem refers to the rocks formed during that time.