1. GEOLOGIC HISTORY, FOSSILS, & RELATIVE DATING

2. Geologic History Uniformitarianism Catastrophism
The idea that the same geologic processes that are shaping Earth today have been at work throughout Earth’s history.
Catastrophism
The principle that states that all geologic change occurs suddenly.

3. What kind of rocks are these fossils in?
Which layer is oldest?
Which layer is youngest?
How do you know?

4. ROCKS TELL A STORY Rocks can tell where they were made and when
Sedimentary rocks can have fossils in them
Rocks can tell when mass extinctions happened
STUDY AND COMPARISON OF ROCK LAYERS OR STRATA IN THE 19TH CENTURY LED SCIENTISTS TO BELIEV THAT A CORRELATION EXISTS BETWEEN PLACE AND TYPE OF ROCK

5. PALEONTOLOGY the study of fossils  remains of ancient life
Body fossils vs. trace fossils
Body = remain of organism, like bones;
Trace = evidence of organism, like footprints
Scientific dating
Absolute dating (gives age in years) Radiometric / radioactive dating (isotopes)
Relative dating (gives age before, after, during) Observation of rock layers
Radiometric dating: use the natural radioactivity of certain elements found in rocks to help determine their absolute age- the use of half-lifes to determine the absolute age of a sample.
In radioactive dating, scientists calculate the age of a sample based on the remaining radioactive isotopes.
Radioactive elments decay into nonradioactive elements at a steady rate which is measured in a unit called half-life.

6. FOSSILS
Traces and preserved remains of ancient life found within rock layers
Fossils show:
Biodiversity
How species have changed over time
Correlation between rock layers from around the world
Relative ages to particular strata
Evidence for the geological time scale
Traces are footprints, droppings, or any other type of evidnece an organism might leave behind
How fossils form:
Dead organisms are buried by layers of sediment, which forms new rock. Then the preserved remains may be discovered and studied.

7. RELATIVE DATING & AGE
Relative Dating: putting rocks and geological events in correct chronological order
Relative Age: how old something is in comparison to something else
Geologic Column: an ideal sequence of rock layers based on relative age with the oldest on the bottom HOW?
Use of sedimentary rocks
Use of fossils
Study of strata

8. ABSOLUTE DATING Examples of how absolute dating is used:
Radioactive Decay
Half-life: the time that it takes for half of the unstable atoms in a sample to decay p.132
Any method of measuring the age of an event or object in years

9. Using Half-Lives to Date Fossils – p. 132

10. INDEX FOSSIL
Fossil that defines and identifies geologic periods; often in only one layer of rock
Easily recognizable
Short-lived (found only in a few layers of rock worldwide)
Wide distribution (geographic range)

11. Ex/ INDEX FOSSIL: AMMONITE
Ammonite fossils are found worldwide, but they existed for only a very specific period of time
this means ammonites are found in very specific layers of rock
when an index fossil is found, the age of the rocks it is preserved can be determined
Traces are footprints, droppings, or any other type of evidnece an organism might leave behind
How fossils form:
Dead organisms are buried by layers of sediment, which forms new rock. Then the preserved remains may be discovered and studied.

12. What kind of rocks are these fossils in?
Which layer is oldest?
Which layer is youngest?
How do you know?

13. LAW OF HORIZONTALITY
Sediments are originally deposited in horizontal layers
Folds or inclines: layers must have been deformed after they were deposited.

14. LAW OF SUPERPOSITION
For undisturbed rocks, the oldest layer is on the bottom and the youngest is on top (Supai is oldest)

15. LAW OF SUCCESSION Fossils are found in a predictable sequence
Fossils in rock B are older then fossils in rock A

16. LAW OF INCLUSIONS
If a rock body (Rock B) contained fragments of another rock body (Rock A),
then Rock B must be younger than the fragments of rock it contained

17. GEOLOGIC TIME SCALE
a series of time intervals that divides Earth’s history
Each layer of rock represents specific interval of time
Index fossils help determine specific period
Time periods divided by specific events like mass extinctions