Geologic Time

What is Relative Age

refers to the age of a rock or fossil in relation to the ages of other rocks or fossils.

What is absolute age in geology?

Absolute age refers to the actual age of a rock, fossil, or geological event measured in years.

What principles are used to determine relative ages of rocks and structures

• Law of Superposition

• Principle of Original Horizontality

• Principle of Cross-Cutting Relationships

• Principle of Inclusions

• Faunal Succession

Principle of Original Horizontality

Layers of sediment are originally deposited horizontally.

Principle of Cross-Cutting Relationships

If a geological feature cuts through another, the feature that is cut is older.

Principle of Inclusions

Any rock fragments (inclusions) within a rock must be older than the rock containing them.

Faunal Succession

Fossil organisms succeed one another in a definite and recognizable order, allowing for the relative dating of rock layers based on their fossil content.

What are Unconformities

surfaces that represent a gap in the geological record, showing times where deposition stopped, erosion occurred, or no sediment was deposited.

What are types of Unconformities

Angular, Disconformity, and Nonconformity

Angular Unconformity

This occurs when younger rock layers are deposited on top of older, tilted, or folded rock layers.

Disconformity

This type is characterized by a gap between parallel rock layers, indicating a period of erosion or non-deposition.

Nonconformity

This happens when sedimentary rocks are deposited on top of older igneous or metamorphic rocks.

What is Stratigraphic column

a graphical representation of the vertical arrangement of sedimentary rock layers, showing their thickness, composition, and the sequence in which they were deposited.

What is Correlation

refers to the process of establishing a relationship between rock layers (strata) from different locations based on their age, composition, fossil content, or other geological features.

What are the Eons and eras of Phanerozoic Eon (the last 541 million years)

Paleozoic Era, Mesozoic Era, and Cenozoic Era

What era was the extinction of dinosaurs

Mesozoic Era

What era marked the emergence of marine life

Paleozoic Era

What era is the age of mammals/animals

Cenozoic Era

What is Radiometric dating

a method used to determine the age of rocks and fossils by measuring the decay of radioactive isotopes contained within them.

What is Radioactive decay

the process by which an unstable atomic nucleus loses energy by emitting radiation.

What is an isotope

a variant of a chemical element that has the same number of protons but a different number of neutrons in its nucleus.

What are parent isotopes

a parent isotope is the original unstable isotope that undergoes decay

What are daughter isotopes

a daughter isotope is the product of the decay process

What is Half-life

the time required for half of the quantity of a radioactive substance to decay into its daughter isotopes