Geologic Time Flashcards
Nonconformity
Unconformities that separate igneous or metamorphic rocks from overlying sedimentary rocks
Angular Unconformity
Formed when originally horizontal rocks are deformed, uplifted, and eroded
Disconformity
A type of unconformity which exists between parallel layers of sedimentary rocks
*Relative Age
The approximate age of a specific rock layer
Uniformitarianism
The theory that changes in the earth’s crust during geological history have resulted from the action of continuous and uniform processes
Original Horizontality
All rock layers are originally laid down (deposited) horizontally and can later be deformed
Original Continuity
Layers of sediment initially extend laterally in all directions
Superposition
Within a sequence of layers of sedimentary rock, the oldest layer is at the base and that the layers are progressively younger with ascending order in the sequence
Cross Cutting Relationships
A principle of geology that states that the geologic feature which cuts another is the younger of the two features
Baked Contacts
Rock encountering molten rock, lava or magma, will become cooked or changed (metamorphosed)
Inclusions
Any rock fragments in a sedimentary layer must be older than the layer
*Unconformity
When an older rock formation has been deformed or partially eroded before a younger rock layer, usually sedimentary, is laid down
Correlation: Lithologic vs. Fossil
Lithological correlation is a procedure, decisive what layers (strata) in geological cross-sections located in different places belong to the same geological body now (or belonged in the past), while fossil correlation states that like assemblages of fossils are the same age and therefore strata containing these particular fossils are also the same age.
*Radiometric Dating
Calculates an age in years for geologic materials by measuring the presence of a short-life radioactive element
Isotope
Atoms with the same number of protons but different numbers of neutrons
