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(Radioactive dating)…read more

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Radioactive Isotopes
"Clocks in Rocks"
A numerical (or "absolute")
age is a specific number of
years, like 150 million years
ago. A relative age simply
states whether one rock
formation is older or younger
than another formation.
The Geologic Time Scale
was originally laid out using
relative dating principles.…read more

Slide 3

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"Clocks in rocks"
Radioactive "parent" isotopes spontaneously decay to
form new "daughter"isotopes while releasing energy.
For example,
decay of the parent isotope Rb-87 (Rubidium) produces a
stable daughter isotope, Sr-87 (Strontium), while releasing a
beta particle (an electron from the nucleus).
("87" is the atomic mass number = protons + neutrons.)
K-40 (Potassium) decays to Ar-40 (Argon)
C-14 (Carbon) decays to N-14 (Nitrogen)…read more

Slide 4

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Get a "half-life"!
Radioactive Half-Life -
The time taken for half the
number of unstable parent
radioactive nuclei in a sample
to decay to stable daughter
Example: K - 40Ar = 1,200 million years…read more

Slide 5

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Determine the half-lives for the other three isotopes
U-235 Half-life = 713 Million Years U-238 Half-life = Million Years
Rb-87 Half-life = Billion Years C-14 Half-life = Years…read more

Slide 6

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Radiocarbon (14C) Dating
The radiocarbon dating
method was developed in
the 1940's by Nobel Prize
winner Willard F. Libby.
It evolved into the most
powerful method of
dating late Pleistocene
and Holocene artefacts
and geologic events up to
about 50,000 years in age.…read more

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