Geologic Time

Geologic Time

The timeline of Earth's history, divided into eons, eras, periods, and epochs.

Relative Dating

Determining the age of rocks and fossils in relation to one another.

Absolute/Numerical Dating

Determining the precise age of rocks using radiometric techniques.

Superposition

In a sequence of undisturbed sedimentary rocks, the oldest layers are at the bottom.

Faunal Succession

The use of fossil organisms to date rock layers.

Unconformity

A gap in the geologic record, indicating periods of erosion or non-deposition.

Angular Unconformity

An unconformity where younger sediment layers are deposited on tilted or eroded older layers.

Radioactive Decay

The process used in absolute dating to determine the age of rocks.

Half-life

The time required for half of the radioactive nuclei in a sample to decay.

Correlation of Rock Layers

The technique of matching rocks of similar ages from different regions.

Metamorphism

The process by which existing rock is altered by heat, pressure, and chemically active fluids.

Sedimentary Rocks

Rocks formed from the accumulation and compaction of mineral and organic particles.

Eon

The largest division of geologic time.

Epoch

A subdivision of a period in the geologic time scale.

Holocene Epoch

The current epoch in the geologic time scale, starting around 11,700 years ago.

Cretaceous Period

A period in the Mesozoic era known for the dominance of dinosaurs before their extinction.

Meteorite Samples

Rock samples from meteorites that are often dated using radiometric techniques.

Paleozoic Era

A major era of geologic time that lasted from about 541 to 252 million years ago.

Proterozoic Eon

The eon before the Phanerozoic, lasting from about 2.5 billion to 541 million years ago.

Cambrian Period

The earliest period of the Paleozoic era, known for a rapid diversification of life.