Earth Science Geologic Time Scale

A system to classify Earth's 4.55 billion-year history into time periods.

The largest division of geological time, such as the Precambrian.

A subdivision of an eon, like the Cenozoic era.

A subdivision of an era, for example, the Jurassic period.

The smallest subdivision of geologic time, such as the Holocene epoch.

A method to determine the age of rocks by comparing them with others.

A gap in the geological record, indicating erosion or non-deposition.

Remains of organisms used to study Earth’s biological history.

The creation of Earth occurred approximately 4.55 billion years ago.

The earliest known single-celled life appeared between 4.00 and 3.50 billion years ago during the Archean Eon.

The first signs of plate tectonics occurred around 3.00 billion years ago in the Archean Eon, indicating early geological activity.

Multi-cellular organisms emerged around 1.00 billion years ago during the Proterozoic Eon, evolving from single-celled ancestors.

A period between 850 and 635 million years ago during the Proterozoic Eon when Earth was mostly covered in ice.

The rapid emergence of major animal groups occurred approximately 535 million years ago, marking a pivotal event in the Cambrian Period.

A geological time period that lasted from 2.5 billion to 541 million years ago, noted for the first multi-cellular life forms.

A geological eon that spans from 4.0 to 2.5 billion years ago, known for the earliest life forms and the start of plate tectonics.

An extinct marine arthropod that lived during the Cambrian period.

A mass extinction event occurring 460 - 430 million years ago, marking the end of the Ordovician period.

Early ancestors of amphibians, like Tiktaalik, emerged around 375 million years ago.

Reptiles became the dominant land species around 320 million years ago in the Carboniferous period.

A supercontinent that formed around 300 million years ago during the Carboniferous period.

A geological timeframe occurring 419 - 359 million years ago, known as the 'Age of Fishes'.

A rapid loss of a large number of species within a relatively short time frame.

The vast ocean that surrounded Pangaea, existing during the time of the supercontinent.

The mass extinction event 65 million years ago that wiped out the dinosaurs and giant marine reptiles due to an asteroid impact.

The earliest nocturnal mammals that evolved after the dinosaurs, leading to hominids and eventually modern humans.

The geological era following the dinosaurs where mammals, including primates, became dominant.

An early hominid species known for the fossil 'Lucy', which lived around 3.2 million years ago.

A mass extinction event that occurred around 201 million years ago, leading to the dominance of dinosaurs.

The largest mass extinction event approximately 252 million years ago, which eliminated 90% of species.

The largest extinction event in Earth's history, occurring at the end of the Permian Period.

Mammal-like reptiles that evolved into the first mammals around 220 million years ago.

A mass extinction event 201 million years ago that eliminated 80% of species on land and sea.

The period following the Triassic, noted for the dominance of dinosaurs and the evolution of the first birds.

The first known bird that evolved from feathered dinosaurs around 160 million years ago.

The last period of the Paleozoic Era, ending with the Great Dying.

The first period of the Mesozoic Era, after the Permian, where dinosaurs began to emerge.

A framework to divide Earth's history into manageable time intervals.

The earliest eon in Earth's history before the Cambrian period.

The current epoch, starting approximately 11,700 years ago.

Establishing the age of rocks by comparing them to others.

A break in the geological record indicating missing time.

The information about past life forms derived from fossils.