Relative Age Dating Flashcards
How is geologic time recorded? Hint: GEO
Recorded by rocks, every layer records the period of time during which it formed
What are rock layers like?
Pages in a book since there is a chronological order, a start and finish
What are the two different ways to determine a rock’s age?
Relative age dating and Absolute age dating
What is relative age dating?
Age in relation to another thing, a sequence of events
What is absolute age dating?
A Specific numerical age
What did Aristotle believe about fossils?
He never realized that fossils were once living, “A great many fishes live in the earth motionless and are found when excavations are made”
What did Nicholas Steno do?
He was the founder of stratigraphy, the study of rock layers and layering, realized fossils were once living
What did many believe before Nicholas Steno’s findings?
Rocks that were formerly termed “Tongue stones” were actually shark teeth, Steno realized tongue stones were shark teeth
What are the 4 principles of stratigraphy that affect the relative age dating of rocks?
Each must be accounted for in age dating
1)Superposition
2)Original Horizontality
3)Cross Cutting
4)Inclusions
Steno’s principles of stratigraphy are concerned with determining an order of events. T/F
True
What is the principle of superposition?
It states that each rock layer is younger than the one below it
How do sedimentary rocks form when they become layers?
They are originally flat-lying layers, the oldest at the bottom and the youngest at the top
What does the principle of original horizontality state?
Sedimentary rocks are originally flat layers, if they are slanted/inclined then something must have happened to them
What can cause the folding of layers to cause them to not be flat-lying?
The squeezing along plate boundaries can change this, resulting in the folding of layers
What does the principle of cross-cutting state?
Younger features of the rock cut across older features
What does the principle of inclusion state?
Inclusions of another rock type must have come from an older rock body
Rock pieces INSIDE another rock is OLDER
What are the 5 fundamental geological events that affect the relative age dating of rocks?
1) Deposition
2) Erosion
3) Intrusion
4) Faulting
5) Deformation
What is intrusion?
Refers to the injection of magma into previously deposited sedimentary rocks, cross-cutting relationships govern their age
MAGMA INTRUDES ON EXISTING ROCK LAYERS
What can magma do when it intrudes upon rocks?
It can either be sills or dikes
What is a sill?
Magma intrusions that are PARALLEL to the layering
What is a dike?
Magma intrusions that are CUTTING ACROSS layers
What is faulting?
Refers to the breaking and offset of previously deposited sedimentary rock layers
How are faults and fractures different?
Fractures show no visible offset, while faults do
What is deformation?
Refers to any sort of tilting, folding, or rotation of sedimentary rock layers, deformed layers are no longer horizontal
What are unconformities?
Represents a long period of time for which no rock is preserved, erosion removes previously formed rocks
Doesn’t have to be erosion, it can be a hiatus
What are the 3 basic types of uncomformities?
Nonconformity: SEDIMENT OVER IGNEOUS OR METAMORPHIC
Angular Conformity: SEDIMENTARY OVER SEDIMENTARY BUT AT DIFF ANGLES
Disconformity: SEDIMENTARY OVER SEDIMENTARY, PARALLEL, BUT TIME MISSING
How do nonconformities form?
Deposition of sediments on top of older igneous or metamorphic rock
How does angular unconformities form?
Formed when flat layers are folded, eroded, and new sediment is deposited on top
How do disconformities occur?
When erosion has removed previously deposited layers, leaving a gap in time
What type of unconformities does the Grand Canyon have?
ALL 3
What unconformity exists between the Tapeats Sandstone and the Underlying Vishnu Schist?
Nonconformity
The Tapeats Sandstone still represents the same unconformity even though one is angular and one is non conformity. T/F
TRUE
