Geological Time Flashcards
How old is the Earth?
4.5 billion years old
When did life begin
4 billion years ago
What is the Principle of Superposition
oldest layer at the bottom, youngest layer at the top
What is Stratigraphy
overall package of rock
What is Strata
individual layers
What is the Principle of original horizontality
tilted rocks indicate a crustal disturbance. Happens after the rock forms.
What is the Principle of Original Lateral Continuity
Rocks that eventually get separated by a valley or something else. Same rock lies on either side
What is Actualism/uniformitarianism
“The present is the key to the past”
What is an Unconformity
“Hiatus” in the rock record. Like a missing page out of a book
What are the 3 different types of unconformities
- Nonconformity
- Disconformity
- Angular
What is Nonconformity
Sediments that come from weathering sit on top of older igneous rocks. Nonconformity is the period of uplift/erosion that expose the deep rocks at the surface. (gap in the record)
What is disconformity
Irregular surface caused by weathering is eventually covered by a new layer. (See slide 12 in presentation 1)
Angular disconformity
The land folds severely, weathers, and then is covered again. Easiest one to recognize.
Pluton
Magma Chamber. Cools and forms dikes
Dike
A rock that cross cuts other rocks (igneous)
Concept of inclusion
Whichever rock is “included” in the other rock is the older one.
Biostratigraphy
Physical fossils, or trace fossils. Proves that life on earth was unique to each time period.
Bioturbation
Fossils of the tracks made by organisms. (Trace fossils)
Principle of Biologic Succession
rock unit formations could be identified by the fossils present in that rock.
Radioactive dating
Uranium half life is 4.5 billion years old.
Uranium-238 (Parent isotope)
Lead-206 (Daughter isotope)
With time, you lose more and more parent isotope material. We can age rocks by using this.
