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Radiometric Dating
Chapter 17 section 1
(This is transcribed from a read only slide show.)
Geologic Time Scale:
Slide Number
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Information
___________________ pinpoint the
time in history when something took
place – for example the extinction of
the dinosaurs about 65 million years
ago.
An understanding of
_______________ allows us to
accurately determine numerical dates
for rocks that represent important
events in Earth’s vast history.
Every atom has a _________ that
consists of ______ and __________.
Each proton has a positive electrical
charge and each neutron is neutral
because it contains a _____________
and a ___________ charge.
Negatively
charged________________ orbit
the nucleus.
Each chemical element on the periodic
table is defined by the number of
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protons in its nucleus, which gives the
____________________.
The atomic number of carbon is 6
because it has 6 protons in the
nucleus. Zinc always has 30 protons in
the nucleus, so its atomic number is
30.
Practically all of an atom’s mass is in
its nucleus, indicating electrons have
practically no mass. By adding
together the number of protons and
neutrons in the nucleus, the
______________ is determined.
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The number of neutrons in the nucleus
can vary. These variants, called
_________, have different mass
numbers. Carbon has two well-known
isotopes.
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How many protons and neutrons does
the nucleus of carbon-12 contain?
Nucleus of carbon 12
Atomic number = ______
Number of Protons= ______
Number of Neutrons=______
How many protons and neutrons does
the nucleus of carbon-14 contain?
Number of Protons= ______
Number of Neutrons=______
One isotope of the element Uranium is
U-238. How many protons and
neutrons are in its nucleus?
Protons=_________
Neutrons=________
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The nuclei of some isotopes are
unstable and spontaneously change to a
different element. This process is
called ____________.
What happens when unstable nuclei
decay? One possibility is the emission
of an _______________.
An alpha particle consists of
___________ and
_______________.
For each alpha particle emitted, how is
the mass number of the radioactive
isotope affected?_____
How is the atomic number of the
radioactive isotope
affected?___________
Another type of radioactive decay is
the emission of a ____________,
which is an electron that was part of a
neutron.
When a beta particle is
____________, a neutron becomes a
proton.
For each beta particle emitted, how is
the mass number
affected?_________
How is the atomic number affected?
_____
A third type of radioactive decay is
___________
____________.
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The captured electron combines with a
proton to form a ___________.
When an electron is captured by a
nucleus, how is the mass number
affected?___________
How is the atomic number affected?
_______
In each type of ________________,
the number of protons in the nucleus,
and thus the atomic number of the
radioactive isotope, changes.
When Uranium-238 decays to
Thorium-234, what type of decay must
take place?________
When Thorium-234 changes to
Protactinium-234, what type of
radioactive decay must
occur?___________________
________________________
When Uranium-238 decays, it emits 8
alpha particles and 6 beta particles
before finally becoming the stable
daughter product.
What is the atomic number and mass
number of the daughter product?
Atomic number=___________
Mass number= ____________
Before the stable end product, Lead206 (Pb-206), is reached, many
different isotopes are produced as
intermediate steps.
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The reason that radioactivity is a good
“clock” for determining reasonably
accurate numerical dates is that the
rate of decay for each radioactive
isotope is constant and can be
accurately measured.
857
The rate of radioactive decay for each
unstable isotope is expressed as its
_______________.
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________ is the time required for
one-half of the nuclei in a sample to
decay. The graph shows what occurs
when a radioactive isotope decays
directly to its stable daughter
product.
After one half-life,
_________________ atoms have
decayed to the stable daughter
product. The number of radioactive
parent atoms and stable daughter
product atoms is the same.
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After a second half-life, half the
remaining radioactive atoms will decay.
Compared to the number of
radioactive atoms at the beginning,
there are now only one-quarter (1/4)
as many.
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After the third half-life the fraction
of the original radioactive atoms
remaining will be one-eighth (1/8).
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Notice that the percentage of
radioactive atoms that decay during
one half-life is always the same: 50%.
However, the actual number of atoms
that decay with the passing of each
half-life continually decreases.
What is the age of a sample if the
ratio of radioactive parent to stable
daughter product is 1:1 and the halflife is 5 million years?__________
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What is the age of a sample containing
the same hypothetical isotope if the
parent-daughter ratio is
1:7?__________
Sedimentary rock can seldom be dated
directly by radiometric means
because. . .
. . .the particles composing most
sedimentary rocks come from rocks of
diverse ages.
By contrast, the crystals in an igneous
rock all form at about the same time.
_______________________ for
sedimentary layers are usually
determined by examining their
relationship to igneous rocks.
Therefore, the age of the Devonian
shale must be greater than 370 million
years and less than 400 million years.
What is the age of rock layer K?
Older than _______ million years.
Younger than _______ million years.
What can you say about the rock
layers L, I and E?
Older than ______ million years.
Younger than ______ million years.
Which statement about the numerical
age of layer J is correct?_________