Earth's History & Geological Time Vocabulary

Vocabulary flashcards covering Earth's age, the structure of geologic time, major eras, key events, and fundamental geological principles based on the study guide.

Radiometric Dating

A technique used by scientists to determine Earth's age by measuring radioactive decay in ancient meteorites and the oldest Earth rocks.

Relative Dating Techniques

Methods used to determine the age of Earth and rock layers based on the layering of rock strata.

Eon

The broadest slice of geologic time, lasting billions of years long.

Era

A subdivision of an eon marked by major changes in life forms and mass extinctions.

Period

A subdivision of an era based on specific rock layer systems.

Epoch

The shortest unit of geologic time, defined by detailed changes in climate or specific fossil records.

Precambrian Time

The timeframe from $4.5\text{ billion}$ to $541\text{ million}$ years ago that covers $88\text{\%}$ of Earth's history, during which Earth formed, cooled, formed oceans, and single-celled life appeared.

Paleozoic Era

The era from $541$ to $252\text{ million}$ years ago nicknamed the 'Age of Invertebrates & Amphibians', featuring the Cambrian Explosion and ending with the Permian Extinction.

Cambrian Explosion

An event during the Paleozoic Era that created massive diversity among life forms.

Permian Extinction

The largest mass extinction in history, which marked the end of the Paleozoic Era.

Mesozoic Era

The era from $252$ to $66\text{ million}$ years ago nicknamed the 'Age of Reptiles', during which Pangea broke apart and dinosaurs lived until the K-T Extinction.

K-T Extinction

A catastrophic event caused by a massive asteroid impact that wiped out dinosaurs and marked the end of the Mesozoic Era.

Cenozoic Era

The era from $66\text{ million}$ years ago to the present nicknamed the 'Age of Mammals', characterized by ice ages, modern continental movement, and the evolution of human species.

Law of Superposition

A geological principle stating that in undisturbed sedimentary rock layers, older rocks and fossils are at the bottom and younger layers are at the top.

Index Fossils

Fossils of organisms that were widespread, abundant, and only lived for a short period of time (such as Trilobites), used to date rock layers.

Mass Extinctions

Catastrophic events that wipe out a large percentage of Earth's species, marking the boundary between eras.