Historical Geology Vocab

Uniformitarianism

The idea that Earth has always changed in uniformed ways and that the present is the key to the past

Relative Dating

An estimate whether an object is younger or older than other things found at the site

Unconformity

a surface that separates two rock masses or strata of different ages, indicating a gap in the geologic record

Correlation

the process of matching and connecting rock layers or geological formations across different locations to determine their age and relationship

Law of Superposition

in undisturbed sedimentary rock layers, the oldest layer is always at the bottom, and the youngest layer is at the top

Principle of Original Horizontality

sedimentary rock layers are initially deposited in horizontal or nearly horizontal planes, and parallel or nearly parallel to the Earth's surface

Principle of Cross-Cutting Relationships

any geological feature that cuts across or disrupts another feature is younger than the feature it cuts

Fossil

remains or traces of ancient organisms preserved in rock, often used to date the rock layers in which they are found.

Index Fossil

a fossil used to determine the relative age of rock layers

Extinct

species that no longer exist on Earth due to various factors such as environmental changes or human activities.

Evolution

the gradual change in species over time through processes like natural selection and genetic variation.

Ice Age

a period of long-term reduction in temperature on Earth, leading to the expansion of continental ice sheets and glaciers.

Radiometric (Absolute) Dating

a method used to determine the age of rocks and fossils based on the decay of radioactive isotopes.

Radioactivity

the emission of radiation from unstable atomic nuclei.

Half-Life

the time required for half of the radioactive atoms in a sample to decay, allowing scientists to estimate the age of materials.

Radiocarbon Dating

a specific method of radiometric dating that uses the decay of carbon-14 to determine the age of organic materials up to about 50,000 years old.

Geologic Time Scale

a system that categorizes Earth's history into a series of chronological intervals based on significant geological and biological events.

Eon

the largest division of geological time, spanning hundreds of millions to billions of years, encompassing several eras.

Era

a subdivision of geological time within an eon, typically lasting tens to hundreds of millions of years, marked by distinct geological and biological changes.

Period

a division of geological time within an era, generally lasting tens of millions of years, characterized by specific rock formations and significant events in Earth's history.

Epoch

a division of geological time within a period, lasting millions of years, marked by notable climatic and evolutionary changes.