1. Geology and Earth's History...

2. The Age of Enlightenment:
End of the 18th century (1700’s)
People began to look to science for answers:
How old is the Earth?
How was it formed?
New ideas were wearing down traditional ideas

3. The Age of Enlightenment:
Beliefs of that time:
Earth was several thousand years old
Earth’s features (mountains, canyons, etc) were caused by rare but quick impacting catastrophes

4. James Hutton (1726-1797) Scottish Lawyer Became a doctor
Successful farmer
Interested and studied Earth’s processes

5. James Hutton Found areas of granite in sedimentary rocks of Scotland
Viewed as evidence of heat beneath the surface
Decided that Earth’s core made new rock

6. Hutton’s drawing and the rock that inspired it at Siccar point
James Hutton
Found unconformities
Areas where layers are not in neat rows
lower layers must have been there long ago, then later moved or pushed up
Evidence of long periods of time in earth's history.
Hutton’s drawing and the rock that inspired it at Siccar point
Photo obtained at:

7. James Hutton Uniformitarianism
What we see changing the Earth today must be the same as what changed the Earth in the past
"Theory of the Earth; or an Investigation of the laws observable in the composition, dissolution, and restoration of land upon the globe." Transactions of the Royal Society of Edinburgh, 1788, 1:

8. Earth’s Geological Processes
Uniformitarianism:
Processes shaping the earth (erosion, deposition, mountain building etc.) do not change over time but remain uniform
Catastrophism:
All geologic processes (locally and globally) occur suddenly due to violent changes in the Earth
vs.
Today we see that both cause changes to the earth.

9. Words to know…
Fossils: remnants of past life/living things; mostly remnants of hard things
Paleontology: the study of fossils
teaches us about changes to life on Earth
integrates Biology and Geology

10. How do geologists know how old rock is?
Law of Superposition: in undisturbed areas, younger rocks lie above older rocks
Relative Dating: comparing
layers of rock to determine the order of formation
Relative Time: time based upon relationships in rock layers; relative order of events

11. Given the colored “rock” layers: * Which layer is oldest?
Relative Dating
Given the colored “rock” layers:
* Which layer is oldest?
* Is the green rock older or
younger than the pink rock?

12. But............... Sometimes things don’t happen uniformly
Geologic Column can help identify the relative age of rock layers.
Diagram from:

13. What’s the order?

14. Stratigraphy Complete the Stratigraphy document
find the relative age of the layers in the rock sequences!

15. Absolute Dating:
A Measure of Time...

16. Establishing the age of an object in numbers of years
Absolute Dating...
Establishing the age of an object in numbers of years
Uses radioactive or radiometric dating

17. T. W. Richards, 1913: found two atomic masses for lead.
F. W. Aston, In 1919: separated neon atoms into two different isotopes
Invented the mass spectrograph
Today: many isotopes of the elements have been discovered.

18. Radioactive elements are unstable and change to become stable
Radiometric Dating
Radioactive elements are unstable and change to become stable
Measuring the amount of breakdown of radioactive atoms in rocks to determine age
Unstable Isotope
Aka “Parent”
Stable Isotope
Aka “Daughter”

19. In this compound, are all the atoms of a given element exactly the same?
Isotopes of an element have the same chemical properties but different atomic weights.

20. Isotopes
Isotopes - Different forms of an element having the same number of protons but different numbers of neutrons (and therefore different atomic weights).

21. Naturally occurring chemical elements are usually mixtures of isotopes, and so their atomic masses are weighted averages of the masses of the isotopes in the mixture.

22. Radioametric Dating
Half-Life- time it takes for 1/2 of the radioactive
atoms to decay into a stable isotope
Rate of breakdown is constant
Unstable isotope is Parent Material; Stable material produced after decay is Daughter Material

23. Radioametric Dating
Living things have a constant ratio of C-14 to C-12
Dead things have their C-14 begin to decay
Half-life for C-14 is 5,730 years
Carbon-14 is mainly used for things up to 50,000 years old

24. Radioametric Dating Half-life for C-14 is 5,730 years
If you have 12 grams of C-14, how long will it take for the parent material to decay into 6 grams?
If you have 24 grams of C-14, how much parent material will be left after 5,730 years?

25. Half Life Ratios 1 half life = ½ radioactive
2 half lives = ¼ radioactive
3 half lives = 1/8 radioactive
4 half lives = 1/16 radioactive

26. DIRECTIONS
Set up a table for the problems that includes Time, Unstable Amount, and Stable Amount
Example: Scientist found a sample of bone and found that 6.25% of the total carbon 14 was left. Determine the age of the bone.

27. Example: Scientist found a sample of bone and found that 6
Example: Scientist found a sample of bone and found that 6.25% of the total carbon 14 was left. Determine the age of the bone. (C-14 Half-life is 5,730 years)
# of Half-lives
Time (yrs.)
Unstable
Stable