1. Geology /

2. Essential Question
How have the geologic sciences developed over time?

3. Catastrophism
Archbishop James Ussher developed a chronology of the world in the mid-1600s
Calculated creation of Earth to have occurred Oct 23, 4004 BC
Chronology eventually printed in notes of many Bibles
Led to principle of catastrophism

4. Catastrophism Earth shaped by major disasters that no longer occurred.
Noah’s Flood for example
Allows Earth to be quite young because its landforms can change quickly

5. Modern Geology In late 1600s, Nicolas Steno developed:
Principle of original horizontality
Law of superposition

6. Modern Geology James Hutton wrote “Theory of the Earth” in 1785.
Offered principle of uniformitarianism.
Claims the same physical processes that occur today occurred in the past
Understanding the present is the key to understanding the past

7. Modern Geology
Hutton wrote, “We have a chain of facts that clearly demonstrates that the materials of wasted mountains have traveled through rivers.”
Claimed only long periods of time were required to shape the Earth as we see it.
Modern geologists have calculated American mountains erode at 3cm/year.
At that rate, a 10,000 ft mountain would erode in 100 million years.

8. It just takes time

9. Modern Geology
In 1821, Louis Agassiz heard another scientist claim there was evidence for glaciers in places where there were currently no glaciers.
He attempted to disprove hypothesis.
He ended up accepting hypothesis and forming a hypothesis of a great ice age.
Provided evidence for uniformitarianism.

10. Glacial valley

11. Geology at work today Geologists impact our world in numerous ways
Engineering geologist help design buildings to withstand earthquakes and other forces
Petroleum geologists help find oil and natural gas
Geology is also an essential part of astronomy, oceanography, paleontology, meteorology and more

12. Check-up
What is catastrophism?
What is uniformitarianism?

13. Essential Question
How can scientists determine ages of geologic material?

14. Relative dating Placing material and events in sequence
Principles and rules of
Law of superposition – oldest rocks are on the bottom
Principle of original horizontality – sediment is deposited horizontally
Principle of cross-cutting relationships – younger feature cuts through an older feature

15. Superposition is well illustrated by the strata in the Grand Canyon

16. Horizontality
Principle of original horizontality claims layers of sediment are deposited horizontally.
So, layers that are folded or otherwise distorted were distorted after they were deposited.

17. Cross-cutting relationships

18. Relative dating Unconformities
An unconformity is a break in the rock record
Types of unconformities
Angular unconformity – tilted rocks are overlain by flat-lying rocks
Disconformity – strata on either side are parallel
Nonconformity – igneous or metamorphic rock uplifted, eroded and then covered by sediment

19. Formation of an angular unconformity

20. Relative dating Principles and rules of Unconformities
Types of unconformities
Nonconformity
Metamorphic or igneous rocks below
Younger sedimentary rocks above

21. Several unconformities are present in the Grand Canyon

22. Correlation of rock layers
Correlation means to show a relationship
Matching rocks of similar age in different regions
Often relies upon fossils

23. Check-up
What is the difference between catastrophism and uniformitarianism?
Do people who believe in catastrophism disagree with the law of superposition?