Relative Age Dating and Geologic Time Flashcards

Flashcards on Relative Age Dating and Geologic Time

Relative Age Measurement

Refers only to the order in which geologic events occurred.

Age in years.

Absolute Age

Sediment usually accumulates in horizontal layers; tilted or folded rocks indicate later tectonic forces.

Principle of Original Horizontality

Sedimentary rocks become younger from bottom to top, unless disturbed by tectonic forces.

Principle of Superposition

A rock must exist before anything can happen to it; faults and igneous intrusions are younger than the rocks they cut.

Principle of Crosscutting Relationships

A rock body containing inclusions of preexisting rocks is younger than the rocks the inclusions came from.

Principle of Inclusions and Components

Groups of fossil plants and animals occur in the geologic record in a definite and determinable order, useful for determining relative ages.

Principle of Faunal Succession

Method that assumes lower layers are older and objects can't be older than their materials; used to determine geologic history.

Relative Age Dating

A U-shaped fold; youngest rocks are in the core.

Syncline

A dome-shaped fold.

Anticline

Represents a long time interval for which no geologic record exists in place; a missing rock layer.

Unconformity

Sedimentary layers above and below the unconformity are parallel.

Disconformity

Tectonic activity tilted older sedimentary rock layers, and younger sediment accumulated on the erosion surface.

Angular Unconformity

Sedimentary rocks lie on igneous or metamorphic rocks.

Nonconformity

Matching rocks of the same age from different localities to assemble a complete and continuous record.

Correlation

Fossils that accurately indicate the age of sedimentary rocks because the organism was widespread and existed for a short time.

Index Fossil

A thin, widespread, easily recognized sedimentary layer deposited rapidly over a wide area.

Key Bed

Refers to age equivalence in rock correlation.

Time Correlation

Refers to continuity of a rock unit in rock correlation.

Lithologic Correlation