Geologic Time and Earth History

These flashcards cover key terms and definitions related to geologic time and earth history as discussed in the lecture notes.

Relative Age

Placing rocks and geologic events in their proper sequence without knowing their actual dates.

Absolute Age

Determining the actual age of a geologic event or rock formation, often expressed numerically.

Catastrophism

The theory that Earth history is shaped by sudden, short, and violent events.

Uniformitarianism

The concept that the present is the key to the past, with the processes occurring today occurring similarly in the past.

Law of Superposition

In an undeformed sequence of sedimentary or volcanic rocks, the oldest rocks are at the bottom and the youngest rocks are at the top.

Principle of Original Horizontality

The principle that layers of sediment are originally deposited horizontally.

Principle of Cross-Cutting Relationships

Younger features cut across older features in geological formations.

Correlation

Matching rock layers of similar ages in different regions.

Unconformity

A break in the geological record representing a period of erosion or nondeposition.

Index Fossil

A fossil that is used to define and identify a particular time period in the geological time scale.

Radiometric Dating

A method of dating geological or archaeological specimens by determining the relative proportions of specific radioactive isotopes present in a sample.

Half-Life

The time required for half the quantity of a radioactive isotope to decay.

Biostratigraphy

Using fossils to establish the age of rock layers and correlate them across regions.

Facies

Distinctive characteristics of sedimentary rock that reflect the environment in which it was deposited.

Transgression

The advance of the sea over land, resulting in a shift of environments and sedimentary products.

Regression

The retreat of the sea from land areas, causing the opposite effects of transgression.

Fossil Succession

The principle that fossil organisms succeed one another in a recognizable order, allowing for the identification of the relative ages of rock layers.