1. Aim: How do scientists read rocks for an exact age?
Do Now: Think about this… If you were standing 10 feet from the wall, and I asked you to walk half the distance to the wall, how close would you be? If I asked you to repeat this process, would you ever reach the wall?

2. Basic Atomic Structure
DO NOT
COPY
Electrons – orbit the nucleus.
Protons – are in the atom’s nucleus.
 Neutrons - are in the atom’s nucleus.

3. How are the three atoms of Hydrogen
I. Isotopes :
the unstable form of
an element; found in all objects (rocks, organisms, everyday objects)
*different number of neutrons
STABLE
UNSTABLE
- PROTON
- NEUTRON
UNSTABLE
How are the three atoms of Hydrogen
different?

4. Describe what is happening in the diagram
II. Radioactive Decay :
- process where an Isotope breaks down losing energy and particles.
- This transforms the Isotope into a new stable element.
- Not affected by outside factors
Describe what is happening in the diagram
(Isotope)

5. III. Parts of Radioactive Decay
a) Unstable Radioactive Isotopes, are called Parents.
b) Stable Decayed elements, are called Daughters.
Looking at the graph, what happens to the number of parents and daughters over time?
How many parents do we start with at time zero?
Daughters?

6. Which color dot represents the Parent elements?
Which represents the Daughters?

7. c) Half – Life (Rate of Decay)
- time required for 50% of the unstable Parent Isotopes to decay (change) into stable daughter elements.
- This time is constant and not affected by outside factors.
- Knowing the rate of decay and the ratio of Parent Isotopes to Daughter elements, we can figure out how old the object is.
cover of your ESRT

8. - 50% or HALF of the parents are lost after each half-life
How many parents do we loose each time?
- 50% or HALF of the parents are lost after each half-life

9. V. Common Isotopes Carbon14
Used to date most recent organic material. (anything once living)
Shortest half-life.
How long is the half-life for Carbon14? How does this compare to the other Isotopes?

10. Examples: Use your ESRT
How many years will it take for two half-lives to pass of C14?
What % of C14 will remain at this point?
Which isotope has the longest half life? What is it?
MAKE A CHART!
11,400 yrs
25% C14 will remain
Rubidium-87 (87Rb)

11. THE CHART THAT MAKES HALF-LIFE EASIER
% Parent Remaining
*Number of years
1/1 (100%) 1
1/2 (50%) 2
1/4 (25%) 3
1/8 (12.5%) 4
1/16 (6.25%)

12. Closure:
After analyzing a rock sample, it was found to have 25% (1/4) C14 and 75% (3/4) N14.
a) How many half-lives has the sample undergone?
Two half-lives.
b) How old is this sample?
11,400 years old.

13. The sample has gone through 3 half-lives
2) A student brought a fossil to a laboratory and by analyzing the radioactive decay of C14 she found there to be (12.5%) 1/8th remaining in the fossil.
a) How many half lives has this sample gone through?
The sample has gone through 3 half-lives
b) What percent of the rock sample has decayed into daughters?
87.5%

14. 3) What is the half life of Strontium 90?
25 years

15. Take a worksheet from the back top bin