Week 4: Geologic time Flashcards
What is geological time?
The assigning of an age to rocks, fossils, structures, landscapes and tectonic events.
Name and describe each of the physical principles for calculating relative ages in rocks?
The principle of uniformitarianism - Physical processes we observe today also operated in the past and were
responsible for the formation of geologic features.
The principle of superposition - For undeformed sedimentary rocks/layered igneous rocks: Oldest rocks are on the bottom.
The principle of original horizontality and continuity - Rock layers that are flat have not been disturbed.
The principle of cross-cutting relations - Features that cut across rock layers must form after the rocks
they cut through.
The principle of inclusions - The rock containing the inclusion is younger.
The principle of baked contacts - The baked rock must have been there first (it is older).
Explain the principle of fossil
succession.
A particular fossil species can be found only in a limited interval of strata. Allows for temporal correlation of widely separated strata on the basis of fossil content.
What is an unconformity and a hiatus?
Unconformity – A period of non-deposition and possibly erosion.
Hiatus – The interval of time between deposition of the youngest rock below an unconformity and deposition of the oldest rock above.
Describe and identify this type of unconformity: Angular unconformity.
Describe and identify this type of unconformity: Nonconformity.
Describe and identify this type of unconformity: Disconformity.
Relative age dates – Placing rocks in their proper sequence of formation.
Numerical age dates – Specifying the actual number of years that have passed since an event occurred (known as absolute age dating).
Good to know.
