1. Radioactive Dating

2. Open your notebooks to page 46
Open your notebooks to page 46
Which type of dating is useful for dating young, once living things?
What information can scientists gather form ice cores?
What would keep scientists from using carbon dating on modern fossils?
What 2 characteristic of fossils would make them good index fossils?
Carbon 14 –Radioactive dating
Information about climate changes from the past, and gases that were found in the atmosphere
Nuclear bombs and nuclear activity interfers with carbon dating, so anything after 1940 can not be used for dating
They have to be from a specific time period and found all over the world

3. Radioactive Decay…47 Used to find the absolute age
The rate of decay is measured in half-lives.
A half-life is the amount of time it takes for half of the atoms to change into another form.

4. 2 Common Methods Uranium-238 Carbon -14 Half Life: 4.468 billion years
Half Life: 5730 years
Good for: Determining the age of the “younger” fossils
Note:
dating objects up to 40,000 years old
Only works on things that were once alive (not rocks)
Decays rapidly
Uranium-238
Half Life: billion years
Good for: Determining the age of the “older” fossils
Note:
Used for dating older material (up to 4 billion years)
Decays slowly

5. Parent material 50 % 75 % 87.5 % 93.75% 1st half life 2nd half life
Daughter Material
50 %
75 %
87.5 %
93.75%
1st half life
2nd half life
50 %
3rd half life
25 %
4th half life
12.5 %
6.25 %

6. Carbon-14 has a half life of 5730 years
If you find a fossil that has been through 3 half lives, how old is it?
(5730 x 3 = 17,190)

7. ICE CORE Ice forms layers similar to that of rock
Follows law of superposition
Provides information about climate (thickness of ice layers)
Analysis of the ice tells about the atmosphere (CO2, oxygen, volcanic ash)
An ice core from Antarctica 3km long showed 740,000 years of history and 8 ice ages!!!
ICE CORE