Geologic Time Scale

Flashcards covering key concepts from the Geologic Time Scale, including definitions of major terms and eras.

Geologic Time Scale

A record of life forms and geological events in Earth's history, combining 'geologic' (rock) and 'chronologic' (time) aspects.

Fossils

Remnants, impressions, or traces of animals or plants from a past geologic age preserved in Earth's crust.

Fossil Record

The primary source of information about the history of life on Earth.

Eon

The largest division of the geologic time scale, spanning hundreds of millions to billions of years.

Precambrian

The eon lasting from 4600 million years ago to 540 million years ago, covering almost 90% of Earth’s history.

Hadean Eon

The earliest geological eon characterized by extreme heat and the formation of Earth's first crust.

Archean Era

Lasted from 2500 million years ago to 4600 million years ago, with the earliest life forms, such as bacteria, emerging.

Proterozoic Era

Lasted from 540 million years ago to 2500 million years ago, when marine invertebrates were common.

Paleozoic Era

The era from 570 million years ago to 250 million years ago, known as the age of invertebrates.

Mesozoic Era

Lasted from 250 million years ago to 65 million years ago, also known as the age of reptiles, including dinosaurs.

Cenozoic Era

From 65 million years ago to the present, known as the age of mammals.

Cambrian Explosion

A significant increase in the diversity of life forms around 544 million years ago during the Cambrian period.

Permian Extinction

The largest mass extinction in Earth's history, occurring between 300 million and 250 million years ago.

Triassic Period

The period when dinosaurs began to appear, lasting from 250 million years ago to 200 million years ago.

Jurassic Period

Known as the golden age of dinosaurs, lasting from 200 million years ago to approximately 145 million years ago.

Cretaceous Period

The final period of the Mesozoic era, lasting from 145 million years ago to 66 million years ago, ending with a mass extinction.

Tertiary Period

A period in the Cenozoic era when Earth’s climate was warm and mammals evolved to fill ecological niches available after the dinosaurs.

Quaternary Period

The most recent period of the geologic time scale, from 1.8 million years ago to the present, characterized by ice ages.

Epoch

The smallest division of the geologic time scale, with subdivisions like the Pleistocene and Holocene under the Quaternary.