Geological Time periods

An informal grouping of the majority of Earth's lifespan, and includes ~90% of all time.

(4.6 - 4.0 Ga) The time of the Earth and Moon's creation is characterized by a molten surface and constant bombardment by asteroids

(4.0 – 2.5 Ga)The cooling of the Earth's crust, the formation of the first continents, and the appearance of the earliest single-celled life.

(2.5 Ga – 539 Ma) Oxygen begins to accumulate in the atmosphere. Multicellular life and eukaryotes emerge toward the end of this eon.

(539 Ma – Present) This is the eon of "visible life," where complex multicellular organisms became abundant in the fossil record. It is divided into three major eras:

Spanning from 539 to 252 Ma, this era saw the diversification of marine life and the transition of plants and animals to land.

Rapid diversification of life

First land plants and widespread marine invertebrates.

Diversification of jawed fish and early vascular plants.

Often called the "Age of Fishes"

Known for vast coal-forming swamps; divided in the U.S. into the Mississippian and Pennsylvanian periods.

Ends with the largest mass extinction in Earth's history

Known as the "Age of Reptiles," this era lasted from 252 to 66 Ma

Appearance of the first dinosaurs and mammals.

Dominance of dinosaurs; appearance of the first birds.

Rise of flowering plants; ends with the mass extinction that wiped out non-avian dinosaurs.

The "Age of Mammals" began 66 Ma and continues today.

Includes the Paleocene, Eocene, and Oligocene epochs. Mammals expand rapidly

Includes the Miocene and Pliocene epochs; characterized by the spread of grassy ecosystems.

The current period, including the Pleistocene (Ice Ages) and the Holocene (the current epoch starting ~11,700 years ago).