The Fossil Record and the Geologic Time Scale

Comprehensive vocabulary flashcards covering the fossil record, evolution, uniformitarianism, and the divisions and chronology of the Geologic Time Scale.

Fossil

The preserved remains or traces of a living thing from the past, formed when an organism dies and is quickly buried by mud, sand, or volcanic ash, followed by hard parts turning into rock over millions of years.

The Fossil Record

The collection of all discovered fossils and where they were found, acting like a vast library of Earth's history documenting life through time.

Strata

The layers of rock where fossils are found; older layers are usually positioned deeper down and are used by scientists to determine relative age.

Oldest Known Fossils

Tiny, simple organisms, such as ancient bacteria, preserved in very old rocks that indicate when life first appeared and what it was like.

Extinction

Periods in Earth's history when certain life forms completely disappear from the fossil record, either gradually or through mass extinction events.

Mass Extinction Events

Occurrences in the fossil record where many different species die out around the same time, such as the extinction of the dinosaurs.

Transitional Fossils

Special fossils that show features of two different groups of organisms, serving as missing links that reveal how one group of organisms evolved into another.

Archaeopteryx

A transitional fossil possessing feathers like a bird but a skeleton like a reptile, demonstrating an evolutionary link between dinosaurs and birds.

Uniformitarianism

The principle assuming that natural laws, including geological processes (erosion, sedimentation, volcanic activity) and biological processes (growth, reproduction, death), operate today exactly as they did in the past.

Geologic Time Scale

A system that distinguishes Earth's history based on life-forms that existed at certain times since the planet's formation, categorized into eons, eras, periods, and epochs.

Period

A basic unit of geological time during which a specific kind of rock system is produced.

Era

A major geological division formed when periods are compacted together according to their shared characteristics.

Eon

The longest geological subdivision, created when multiple eras are grouped together.

Epoch

A geological subdivision into which certain periods are divided.

Precambrian Supereon

The earliest span of Earth's history accounting for more than $85\%$ of its duration, extending from $4.6\text{ billion years ago}$ to $540\text{ million years ago}$.

Hadean Eon

An eon beginning $4.6\text{ billion years ago}$ characterized by the solidification of Earth's continental and oceanic crust.

Archean Eon

An eon beginning $4\text{ billion years ago}$ marked by the evolution of Earth's first life forms.

Proterozoic Eon

An eon dating to $2.5\text{ billion years ago}$ characterized by the appearance of multi-celled animals and the gathering of land masses to form continents.

Paleozoic Era

An era beginning $544\text{ million years ago}$ marked by the explosion of diverse marine life and the largest mass extinction of marine organisms.

Cambrian Period

The earliest period of the Paleozoic Era, beginning approximately $541.0\,\text{MYA}$.

Ordovician Period

A Paleozoic period dating to approximately $485.4\,\text{MYA}$.

Silurian Period

A Paleozoic period dating to approximately $443.8\,\text{MYA}$.

Devonian Period

A Paleozoic period dating to approximately $419.2\,\text{MYA}$.

Mississippian Period

A Paleozoic period dating to approximately $358.9\,\text{MYA}$.

Pennsylvanian Period

A Paleozoic period dating to approximately $323.2\,\text{MYA}$.

Permian Period

The final period of the Paleozoic Era, dating to approximately $298.9\,\text{MYA}$.

Mesozoic Era

An era beginning $245\text{ million years ago}$ that marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction.

Triassic Period

The earliest period of the Mesozoic Era, dating to approximately $251.9\,\text{MYA}$.

Jurassic Period

A period within the Mesozoic Era dating to approximately $201.3\,\text{MYA}$.

Cretaceous Period

The final period of the Mesozoic Era, dating to approximately $145.0\,\text{MYA}$.

Cenozoic Era

The most recent era of the Phanerozoic Eon, spanning from $65\text{ million years ago}$ to the present, marking the age of mammals and early human evolution.

Paleocene Period

A period of the Cenozoic Era dating to approximately $66.0\,\text{MYA}$.

Eocene Period

A period of the Cenozoic Era dating to approximately $56.0\,\text{MYA}$.

Oligocene Period

A period of the Cenozoic Era dating to approximately $33.9\,\text{MYA}$.

Miocene Period

A period of the Cenozoic Era dating to approximately $23.0\,\text{MYA}$.

Pliocene Period

A period of the Cenozoic Era dating to approximately $5.3\,\text{MYA}$.

Pleistocene Period

A period of the Cenozoic Era dating to approximately $2.6\,\text{MYA}$.

Holocene Period

The most recent period of the Cenozoic Era, dating to approximately $0.01\,\text{MYA}$.