1. How can you prove animals and plants lived millions of years ago?
Do-Now
How can you prove animals and plants lived millions of years ago?

2. What is a fossil? Evidence of an organism that lived long ago
Fossils are NOT bones

3. How did Lucy become a fossil?
Buried in mud soon after death
Sediment continued to cover the body over time
Minerals from the lake water & sediment replaced the minerals in Lucy’s bones- making a copy of her bones
More sediment piles on top/around the body, forming rock.

4. Fossil Formation

5. How are fossils exposed?
Lakes, streams, etc. may dry up.
Erosion (soil/rock moved from Earth’s surface by wind/water)
Collision between tectonic plates can uplift land above sea level, exposing sedimentary rock

6. Fossils Exposed

7. Other types of fossilization
Imprints
Amber

8. How do scientist calculate how old a fossil is indirectly and directly
How do scientist calculate how old a fossil is indirectly and directly ? Page

9. Indirect and direct method of calculating the age of a fossil
Indirect method- They estimate the age of the fossil by finding the age of the surrounding rock (strata).
Direct methods- Scientist using radioactive isotopes and Carbon-14 Dating to estimate the age of the fossil

10. Dating fossils Indirect method-
Older fossils deeper down, younger fossils up top

11. *What are radio active isotopes?
*Some elements such as Uranium break down or in other words decay into other elements at a constant rate.
*Ex. Uranium ---(4.5 billion years)--- 1/2 Uranium + ½ Lead
These radio active isotopes help Paleontologist determine the age of fossils.

12. The Fossil is Younger than 4.6 billion years old
Why? There is still more Uranium than there is lead.
If there was more Lead than Uranium it would be older
U>L = younger
L>U=older

13. Scenario
If a Paleontologist finds a fossil, and using radio active dating, he finds the following:
Uranium  25% Uranium + 75% Lead
He knows that it takes 4.6 billion years to make half of Uranium turn into lead.
How old is the fossil?

14. Carbon-14 dating
Scientists look at the ratio of C-12 to C-14 in a fossil.
The half-life of carbon-14 is 5,730 years.
C-14 only good for dating fossils less than 60,000 years old. Why?

15. Dating Fossils We know potassium-40 breaks down into argon-40.
If you know the half-life of P-40 is 1.3 billion years, if you measure a rock with 25% P-40 & 75% Argon-40, how old is the sample?

16. Activity- Copy table “Fossil” # of Potassium-40 (Parent isotope)
# of Argon-40
(Daughter isotope)
# of half lives
Age of Fossil
(show work) 1 2 3

17. Activity in Groups of 4 There are 3 envelopes labeled 1, 2 and 3.
Each envelope represents a fossil and you must figure out the age.
The blue= the parent isotope (potassium-40)
The red= the daughter isotope (argon-40)
Look at the ratio of parent to daughter isotopes to figure out how many half lives have gone by.
Note: The half life for potassium-40 is 1.3 billion years.
Hand in 1 table as a group

18. Extra Practice Problems-Radiometric Dating
1. You find a fossil that has 12.5% C-14 left compared to a living sample. How old is the fossil? (Remember- half life of C-14 is years). Show your work!
2. You find a fossil that has 75% potassium-40 and 25% argon-40. How old is the fossil? (Half- life of P-40 is 1.3 billion years). Show your work!

19. Exit Slip
A paleontologist found a fossil and decided to use radio active dating to determine its age? The radio active element he found in the fossil was potassium. He knows it takes 1.3 billion years for half of potassium to turn into argon. By using radioactive dating he found 3 times more argon in the fossil than potassium. Can this paleontologist say this fossil is younger or older than 1.3 billion years old? Explain