the fossil below is that of a coelophysis and was found in upstate n.y. approximately how old is the...
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The fossil below is that of a Coelophysis and was found in upstate N.Y.
Approximately how old is the rock?
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Scientists made the geologic time scale using fossils and call it a relative time
scale, they can give a range.
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Radioactive Decay: Scientists have devised a way of using the decay rate
of Radioactive Isotopes (Atoms).
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Atoms are supposed to have the same number of protons and neutrons
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No Big deal. Eventually it breaks down into its normal stable self
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Carbon 14 is unstable (parent), while Nitrogen 14(daughter) is stable.
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Carbon 14 is unstable: It has an uneven number of protons
and electrons
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Once the original element changes it can never go back. Whatever is lost by the
“parent” is gained by the “daughter”
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This breakdown is predictable, and is measured in half life which is the time required for ½ (50%) the radioactive element to change to the decay
product.
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If no time has passed that means you have 100% of your original element and 0% new element.
If ONE half life has passed that means you have 50% original and
?
•
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After every HALF LIFE, you cut the original product in HALF.
So after one half life you have 50/50
How much of the original is left after TWO half lives?
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Keep cutting the original in half.
Number of Half lives
Original Product Decay Product
0 100% 0%
1 50% 50%
2 25% 75%
3 12.5% 87.5%
4 6.25% 93.75%
Unstable Stable
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You can tell how old something is by counting how many parent and
daughter isotopes you have.
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For example equal amounts of C 14 and N 14 means it has gone through 1
half life. 5,700 years.
How many years is 2 half lives?
How much C14 is left?
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Half Lives
Original remaining # of years
0
1
2
3
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If 100 grams of pure C 14 starts to decay, how much N 14 will be
created in 11,400 years? How many ½ lives is that?
A 200 gram rock sample contains 25 grams of K 40, what is the age of
this rock?
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A rock sample contains 75% Argon and 25% Potassium. How many half lives have
passed, and how long did it take?
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After three half-lives, how much of the original sample of uranium-238 remains?
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If an original sample of radioactive uranium-238 had a mass of 400 grams, what is the total amount of the uranium-238 sample that would be left after 9 billion years?
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If the half-life of the radioactive material is 1,000 years, what is the age of the sample represented by the diagram?
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Draw what you think the box will
look like after 3 half lives