| Hadean | 4.6 to 4.0 billion years ago | Named after Hades, the ancient Greek god of the underworld. This era is associated with the formation of the Earth and the establishment of its early oceans. |
| Archean | 4.0 to 2.5 billion years ago | The Earth’s crust had begun to solidify, life first appeared, and the Earth’s atmosphere and oceans formed. |
| Proterozoic | 2.5 billion to 541 million years ago | Named for the Greek words for “earlier life”. This era was characterized by the buildup of oxygen in the atmosphere and the development of simple multicellular organisms. |
| Paleozoic | 541 to 252 million years ago | Derived from the Greek words for “ancient life”, the Paleozoic era was when life as we know it took off with an explosion of diversity. |
| Mesozoic | 252 to 66 million years ago | Known as the age of dinosaurs, it was during the Mesozoic era that reptiles and mammals began to evolve, and the supercontinent Pangea began to drift apart. |
| Cenozoic | 66 million years ago to the present | Known as the age of mammals, this era saw the rise of mammals and flowering plants, the formation of the Himalayas and Alps, and the evolution of humans. |
