Deep Time: How Old Is Old?

These flashcards cover key vocabulary and concepts from the lecture notes on geological time and dating methods.

Relative Ages

A determination of age based on the order of formation; allows comparison of older vs. younger geological formations.

Numerical Ages

The actual number of years since an event occurred; provides specific dates for geological events.

Uniformitarianism

The principle that the processes operating today are the same as those that operated in the past.

Original Horizontality

The principle that sediments initially settle horizontally due to gravity.

Superposition

In an undeformed sequence of layered rocks, each layer is older than the one above it and younger than the one below.

Lateral Continuity

The principle stating that layers of sediment initially extend laterally in all directions.

Cross-Cutting Relations

A geological principle indicating that younger features truncate (cut across) older features.

Baked Contacts

A geological relationship where an igneous intrusion cooks the surrounding country rock, indicating the baked rock is older.

Inclusions

The principle that inclusions within a rock are older than the rock itself.

Fossil Succession

The principle that fossil organisms succeed one another in a definite and recognizable order.

Unconformities

A gap in the geological record due to erosion or lack of deposition.

Angular Unconformity

An unconformity where horizontal marine sediments are deformed by orogenesis.

Nonconformity

An unconformity where sedimentary rocks overlie igneous or metamorphic rocks.

Disconformity

An unconformity that occurs within sedimentary layers due to interruption in sedimentation.

Stratigraphic Correlation

The method of correlating rock units from different locations based on their properties and ages.

Numerical Age: Radioactive Decay

The process by which unstable isotopes decay into stable ones, allowing the dating of materials.

Half-Life

The time it takes for half of the unstable nuclei in a sample to decay.

Radiocarbon Dating

A method for determining the age of an object containing organic material by measuring the amount of carbon-14 remaining.

Magnetostratigraphy

The method of dating sediments by comparing magnetic polarity reversals to a reference column.

Fission-track Analysis

A method that measures radioactive decay damage tracks in crystals to determine age.

Deep Time

A concept in geology that describes the immense time scale over which geological events occur.