1. “How can scientists determine the age of rocks and fossils?”
Dating
“How can scientists determine the age of rocks and fossils?”

2. Geologic Principles
Uniformitarianism
The processes occurring today have been occurring since Earth formed
Present Earth not caused by catastrophic events

3. Relative vs. Absolute Dating
Relative Age Dating
Establishes the order of past geological events (ex: A is older than B)
A comparison, not an exact age
Absolute Age Dating
Scientists determine the numerical age of rocks and other objects (ex: Sample A is 4.6 million years old)
Exact age of object

4. Relative vs. Absolute Dating

5. Relative Age Dating Original Horizontality
Sedimentary rocks are deposited in (nearly) horizontal layers
Superposition
In an undisturbed rock sequence, the oldest rocks are at the bottom and each layer above is younger than the rock layer below it

6. Youngest
Oldest

7. Relative Age Dating Cross-Cutting relationships
States that an intrusion or a fault is younger than the rock it cuts across

8. Absolute Age Dating Radioactive Decay
Radioactive elements have unstable nuclei due to their number of neutrons
To achieve stability, radioactive elements emit nuclear particles
“Parent” – the original radioactive element
“Daughter” – the new element

10. Absolute Age Dating Radiometric dating Half-life
Process used to determine the absolute age by determining the ratio of parent nuclei to daughter nuclei in a given sample
Half-life
Amount of time it takes a radioactive element to decay to one half of the original amount.

11. Other Dating Methods
Dendrochronology
Science of comparing annual growth rings in trees to date events and environmental changes

12. Other Dating Methods Key Beds Index Fossils
Sediment layers that serve as a time marker in the rock record, result from volcanic ash or meteorite impact debris
Index Fossils
Remains of living things that are:
Easily recognized
Abundant
Short-lived

13. Relative Dating
What principle states that sediments are deposited in horizontal layers?
Which layer is the oldest in this rock sequence? The Youngest?
What principle helped you answer questions 2?
Is the fault line in this rock sequence older or younger than layer D?