1. Relative and Absolute Dating

2. What is Dating?
When geologists date rocks, they are determining how long ago they formed.
Two ways to do this:
Relative Dating
Absolute Dating

3. Relative Dating
Determining how old something is compared to something else
Use words like “older” or “younger” instead of exact numbers

4. Rules of Dating two rules for dating rocks: This is called the
Stuff on the bottom is oldest and the stuff on the top is youngest
This is called the
Law of Superposition
This only works for sedimentary rocks (sometimes lava flows)

5. Order these layers from oldest to youngest
Youngest layer
Oldest layer

6. Rules of Dating two rules for dating rocks: This is called the
2. If a fault or another rock cuts through a layer it happened after (and is younger than) the layer
This is called the
Law of Cross-Cutting Relations

7. Order the events from oldest to youngest
YOUNGEST LAYER/EVENT
Fault
Gray Layer
Multicolored layer
Tan Layer
OLDEST LAYER/EVENT

8. Absolute Dating Determining how old something is
Use numbers (in millions of years, mya)
Only works for Igneous Rocks

9. How Absolute Dating Works
When magma/lava cools, radioactive elements are incorporated into the minerals
Examples:
-- Potassium 40
-- Uranium 235
Potassium 40 (to Argon 40)
Uranium 235 (to Lead 207)

10. How Absolute Dating Works
These elements begin to decay at a known rate starting when the rock cools
We can measure how much of the element is left
Tells us how much time has passed since the rock formed.

11. What can we learn from this?
 Geologist
Basalt, dated to 80 mya
 T-Rex Fossil
Sandstone
Basalt flow, dated to 100 mya
So when did this T-Rex live?
Between 100 and 80 mya
This may not seem very accurate, but compared to the 4,500 million years the earth has been around it gives us a lot more information than we had before

12. What can we learn from this?
Absolute Dating
Helps us determine the age of the earth
Helps us determine when specific events in the history of the earth happened (ex. Extinction of the dinosaurs)
Relative Dating
Can help us estimate the time span between major earthquakes, storms, tsunamis etc
Can help us determine the order that life forms developed on earth