Earth's History Vocabulary

A collection of vocabulary flashcards covering key concepts related to Earth's history and geology.

Uniformitarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes.

Index Fossil

A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found.

Tilting

The slanting of rock layers from internal forces in the Earth.

Intrusion

An igneous rock layer formed when magma hardens beneath Earth's surface.

Sedimentary Rock

A rock that forms from compressed or cemented layers of sediment.

Relative Dating

Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock.

Superposition

A principle that states that younger rocks lie above older rocks if the layers have not been disturbed.

Unconformity

A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

Absolute Dating

A technique used to determine the actual age of a fossil.

Radioactive Decay

The breakdown of a radioactive element, releasing particles and energy.

Half-life

Length of time required for half of the radioactive atoms in a sample to decay.

Radiometric Dating

The process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products.

Geologic Time Scale

A record of the geologic events and life forms in Earth's history.

Geologic Era

A long and distinct period of history with a particular feature or characteristic.

Geologic Period

Segment of geologic time that subdivides the geologic eras into smaller chunks of time.

Cross-cutting Relationships

Principle stating that a fault or intrusion is younger than the rock it cuts across.

Law of Superposition

The top rock layer and its fossils is the youngest and the bottom is the oldest.

Principle of Inclusions

Objects enclosed in rock must be older than the time of rock formation.