Geologic Time & Fossils Flashcards

Vocabulary flashcards based on lecture notes about geologic time, fossils, and related principles.

Law of Superposition

In undisturbed layers, the oldest rocks are at the bottom and youngest at the top.

Principle of Original Horizontality

Sedimentary rocks are originally deposited in horizontal layers.

Principle of Cross-Cutting Relationships

A feature that cuts through rock layers is younger than the rocks it cuts.

Principle of Inclusions

Rock fragments within another rock are older than the rock containing them.

Fossilization

The process of preserving ancient organisms in rock; commonly found in sedimentary rock.

Requirements for Fossilization

Rapid burial, hard parts, low oxygen, and sediment-rich environment.

Permineralization

A fossilization process where minerals fill in the spaces of an organism's tissues.

Carbonization

A fossil formation process where a thin film of carbon is left behind after organic material decomposes.

Amber Fossil

An organism preserved in hardened tree resin.

Cast Fossil

A fossil formed when sediment fills a mold and hardens into the shape of the organism.

Relative Dating

Compares age without exact numbers.

Absolute Dating

Gives a numerical age.

Index Fossil

A fossil used to define and identify geologic periods; widespread and short-lived.

Trace Fossil

Evidence of an organism’s activity, like footprints or burrows.

Principle of Faunal Succession

Fossil species appear in a consistent vertical order over time.

Unconformity

A gap in the geologic record caused by erosion or non-deposition.

Disconformity

A gap between parallel sedimentary layers due to erosion or lack of deposition.

Angular Unconformity

Tilted or folded rocks overlain by flat-lying layers.

Nonconformity

Sedimentary rock overlying igneous or metamorphic rock.