1. Interpreting Geologic Time “The present is the key to the past”
Earth Science
Mr. Cloud

2. Mr. Cloud at the Hall of Earth located at the AMNH!

3. Two Ways To Date Rocks 1. Relative Age: correlation
2. Absolute Age: “My age is…”

4. Principle of Superposition
In an undisturbed sequence of sedimentary rocks , each bed is older than the one above it and younger than the one below.

5. Principle of Superposition

6. Principle of Cross-Cutting Relationships
When a fault cuts through other rocks, or when magma intrudes and crystallizes, we can assume the fault or intrusion is younger than the rocks affected.

7. Igneous Intrusion
Igneous intrusion: Crawford Notch, White Mountains

8. Faults

9. Unconformity
An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous.
“A missing page from a book.”
There are three types: angular unconformity, disconformity, an nonconformity

10. Angular Unconformity

11. Disconformity

12. Nonconformity

13. Correlation
process by which rocks or geologic events from different places are determined to be the same or similar age

14. 3 Methods of Correlation
1. Similarities in Rocks: “Walking the Outcrop”
2. ***Index Fossils***
3. Volcanic Ash/ Meteorite Deposits

15. “Walking the Outcrop”
Permian reef in Guadalupe Mountains National Park, Texas

16. ***Index Fossils***

17. Volcanic/Meteoritic Deposits
Chicxulub Crater: ~ 65 million years old
Although the Chicxulub crater is buried beneath layers of sediments, gravity and magnetic field data have revealed its three-dimensional structure.