-
Determining the ages of rocks through their contained radioactive elements is known as
______________________ dating.
isotopic dating or geochronology
-
An isotope of a given element has the same atomic number as the element, but a different
__________ ________________.
atomic weight
-
An isotope contains the same number of neutrons as the non-radioactive parent element. True
or false
false
-
U-238 and U-235 are two naturally occurring isotopes of ____________________.
uranium
-
The spontaneous disintegration of the nuclei of an atom is called __________________
___________.
radioactive decay or radioactivity
-
The parent of the U-238/Pb-206 isotope system is ___________.
U-238
-
The daughter of the U-235/Pb-207 isotope system is ___________.
Pb-207
-
The time that it takes a given amount of a radioactive isotope to be reduced by one-half is called
the isotopes ____________.
half-life
-
What is the name of the constant that reflects the rate at which a radioactive isotope decays per
unit of time?
decay constant
-
The number of parent isotopes remaining at time t is what parameter in the equation N = No(e-
t).
N
-
What is in the equation N = No(e-t)?
decay constant
-
Given 100 atoms of an isotope, how many will be left after one half-life?
50
-
Given 100 atoms of an isotope, how many will be left after three half-lives?
12.5
-
What is the following equation called: t = (1/)(ln[(D/P)+1])?
age equation or fundamental age equation
-
What is D in the equation t = (1/)(ln[(D/P)+1])?
amount of daughter product
-
The amount of remaining original isotopic material is represented by what parameter in the
equation t = (1/)(ln[(D/P)+1])?
P
-
What isotope system would you use to date a very young rock?
C-14/N-14
-
What isotope system would you use to date a Pleistocene tree trunk?
C-14/N-14
-
What isotope system would you use to date volcanic deposits containing a dinosaur?
K-40/Ar-40
-
Of the isotopic systems mentioned in this chapter which has the longest half-life?
Rb-87/Sr-87
-
Of the isotopic systems mentioned in this module which has the smallest half-life?
C-14/N-14
-
What kinds of rocks are found at Jack Hills, NW Australia and why are they significant?
- Conglomerate. Detrital zircons were eroded, transported, and then deposited as part of the
- conglomerate. A single detrital zircon was dated at 4.4 b.y. using the U-Pb method.
-
Minerals such as K-feldspar, biotite, and hornblende all contain the element K. What isotopic
system would you use to date these minerals?
K-40/Ar-40
-
What isotopic system would you use to date a crystal of zircon?
U238/Pb206 or U235/Pb207
-
What is the oldest material dated on planet Earth, and what is its age?
Zircon, 4.4 b.y.
-
Where is the oldest material dated on planet Earth?
Jack Hills, NW Australia
-
What and where is the oldest rock dated on planet Earth? What is its age?
Acasta gneiss, NW Canada, 4.03 b.y.
-
What mineral and isotopic system were used to date the oldest detrital crystal and rock on
planet Earth?
Zircon, U-Pb
-
Can you date the age of the Earth from fossils?
- No, the first evidence for life on Earth does not occur until the Archean. In other words, there
- was no life on Earth until approximately 4.0 billion years ago. Without life there can be no fossils.
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