1. Calculating Ages of Solar System objects
Radiometric dating
Cratering
Sequencing

2. ____________________ using radioactive decaysP D
Parent
Element
Daughter
Element
Half-life – __________________________________________.
Examples of radioactive isotopes - ________________ half-life = 4.5 Gyr
232Th half-life = 3.5 Gyr
____ half-life = 6,000 yrs (Carbon dating)
See also pages _______ for more on radiometric dating!

3. Fill this in based on the next slide.
Number of
half lives
Time (years)
Number of Parents
Fraction parents still left
Number of Daughters
# Daughter/ # Parent 1 2 3 4 5

4. Radioactive Decay, cont.
Assume we’re doing Iron-60 dating. It has a half-life of 5 million years
Radioactive Decay, cont.
At time = 0, the rock formed
1 half-life later…
______ yrs total
Clicker question now
After 2 half-lives
______ yrs total
After 3 half-lives
______ yrs total
4 half lives
______ yrs total
5 half-lives
______ yrs total
After 6 half lives …

5. How many parents are left after 2 half lives?8
zero 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

6. Do you think Carbon dating is effective for a 1 million year old fossil?
Yes No
Why or why not?
___________________________________________________________________ 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

7. 5 million years 10 million years 20 million years 30 million years
Element P decays into element D with a half-life of 10 million years. You find 3 times as many daughters as parents. (D/P = 3) How old is the rock?
5 million years
10 million years
20 million years
30 million years
40 million years
I have no clue 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

8. 3,000 years 6,000 years 9,000 years 12,000 years 18,000 years
You find an animal skeleton that has 1/8th as much carbon-14 in it as living samples have. How old is the skeleton?
3,000 years
6,000 years
9,000 years
12,000 years
18,000 years
24,000 years 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80

9. Radiometric dating Any questions? ______________ dating __________:
____________________________ if using __
Radioactive dating
Radioisotope dating.
I won’t call it by these names. These names won’t be on your test.

10. Review: Simplified History
Formation - _____________ ago
Present
______________________________
_________________________________
Recall: 1 Gyr = ___________________
This history was determined by _____________________ ________________________!
How old are the planets in the solar system?
Note: the Sun is ________ years old. It’s ______ burned out.
How much longer will it last?

11. Crater Formation Before ______________! Why is 11 km/sec minimum?
Rocky or icy objects (also called ___ & ___ )
This is going to leave a mark…
Impact site’s ground gets vaporized. So does the impactor!

12. Craters An object this size Will make a crater this big!
Diameter of crater is about ______diameter of rock. Depth of crater is about _________the diameter of rock. See also p. ____

13. Crater _____ These streaks of ejecta are called “_____”.
________________________________ over about _____________ years because _____________________ chemically alters them.
Most prominent under _______________
(at what time, locally?).
So, how can you find the youngest craters on the Moon?
rays

14. Crater Sizes Small < 25 km Big - up to 200 km
Note the central peaks
This puppy is the size of the L.A. basin!
And…

15. REALLY HUGE!! Also known as “multi-ring impact basins”
Similar, but a bit larger crater formed on Mercury, and on the opposite side, we see “weird terrain” see page ____.
That just had to hurt.
Big crater on the Moon

16. How do we measure ages?
Relative dating – Principle of Superposition Ordering of events based on appearance.
Crater counts – surfaces with _______________ are new or old? Why? (see p. ____________)
Radiometric dating of rocks. (see also section 8.5) Called “Carbon dating” when used on recent fossils.

17. Relative Surface Dating – Can you order the events?
A. Volcanic Eruption
B. Fault
C. Crater
D. Hills
Cratered Terrain
(Hint: old or new?
Created when?)
F. Crater
G. Crater

18. A Real Example - Iapetus
What can you say about the age of the small crater?
Landslide?
Smaller Crater
Iapetus is one of Saturn’s moons. Picture taken by Cassini
Crater Rim
Scarp (Shrinkage quake) & subsequent landslide
There is cratering on ground. Do you see many or few craters in this big crater?
What does that tell you about the circled crater?
Is old or new?

19. Iapetus – entire moon Diameter = 1460 km
Here’s the “big crater” we just looked at.
Approx 500 km across
Landslide is here.
Ridge all along equator. Mystery!
In Fall 2009 – the light/dark hemispheres mystery was solved.

20. Ages Now you know how astronomers calculate ages.
Study for the last test.
It is NOT cumulative.