Title: Age Dating Rocks
1Age Dating Rocks
2Two Types of Dating
- Relative Dating
- Absolute Dating
3Relative Dating
4Relative and Absolute Dates
- Relative age states whether one rock formation
is older or younger than another formation. - Absolute age specific number of years. (example
like 150 million years ago.)
5How old is the Earth???
- People used to think that the earth was only a
few thousand years old! - Now we believe that the earth is billions of
years old! video - From Greatest Discoveries with Bill Nye Earth
Science. Discovery Channel School(2005).
Retrieved October 24, 2006, fromunitedstreaming
http//www.unitedstreaming.com/
6Which layer of rock is oldest?
A
B
C!
C
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9Radioactive Decay
10- Radioactive decay is one of Earths sources for
heat.
- Remember
- Accretion
- Differentiation
- Radioactive decay
- Suns radiation
11Before we get to crazy
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1392
of Protons
Atomic Symbol
U
Name of Element
Uranium
238
of Protons Neutons
14- Radioactive decay is the spontaneous change of
the nucleus of an unstable isotope to a stable
one. - Isotope an atom with the same number of protons,
but a different number of neutrons. - As protons and neutrons leave atoms, energy is
produced.
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17- When protons are lost during radioactive decay,
the atom becomes a different element.
- Example When Uranium-238 decays, it loses 32
particles (10 protons and 22 neutrons). What
element is it now?
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19Lead (Pb)!
- What is its new atomic weight? (238-32)
206!
- So, the new product is Lead-206!
- Lead-206 is stable, so it wont decay any further.
20Parents and Daughters
- The original element is called the parent
isotope, and the product of the decay is called
the daughter isotope.
21- The moment an igneous rock crystallizes,
radioactive atoms start to decay to a stable
product.
22- Half life The amount of time it takes for half
of the parent to decay to the daughter.
- After one Half-life, half of the atoms of a
radioactive element will have decayed to a stable
product, and half will remain unchanged.
23Half Life
24- A rock that has a lot of parent, but very little
daughter is very young! - A rock that has a lot of daughter, but very
little parent is very old!
25As the of parent goes down, the of daughter
goes up!
26Radioactive Dating
27How we can get the age
Many minerals contain radioactive isotopes. The
age of any of these minerals can be determined
by 1)counting the number of daughter isotopes in
the mineral, and 2)using the known decay rate to
calculate the length of time required to produce
that number of daughters.
28- Parent Daughter Half-Life
- 14C 14N 5730 years
- 3H 3He 12.8 years
- 40K 40Ar 1.25 Billion Years
- 87Rb 87Sr 48.8 Billion Years
- 238U 206Pb 4.5 Billion Years
29100 g of 14C _at_ time0 Â _at_ 1 half life, 50 g of
14C, 50 g of 14N So 5730 years have passed  _at_
2 half lives, 25 g of 14C, 75 g of 14N So 5730
(x2) or 11460 years have passed _at_ 3 half lives,
12.5 g of 14C, 87.5 g of 14N So 5730 (x3) or
17190 years have passed Total Years Passed 17190
years!
30Lab Radioactive Decay
31Materials
32Procedure
- Obtain all the materials needed for the lab. The
jar represents your rock. The pennies represent
the minerals in the rock. Heads will represent
parents, tails will represent daughters. - Place all 100 pennies in the jar. Imagine that
they are all heads-up (all parents). - Dump the pennies onto the table and separate the
parents from daughters. - Count how many parents and how many daughters you
have. Record the results on a data table. - Place all the parents back in the jar, shake
them, and dump them out again. - Repeat procedures 3-5 until all the parents have
changed to daughters, or until you have only one
parent left. - If you end up with only one parent left, put it
back into the jar, shake it, and no matter what,
imagine it changes to a daughter.
33Data
of Half-lives (one half-life is 1000 years) of Parents of Daughters
1
2
3
4
5
6
7
8
9
10
11
12
34Conclusion
- How many half-lives did it take for all your
parents to change to daughters? - How old is your rock when all the parents have
changed to daughters? - What did you learn from this lab?
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36Known Half-lives