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Geology Geologic Time part
Geology test 3
Determining the ages of rocks through their contained radioactive elements is known as
isotopic dating or geochronology
An isotope of a given element has the same atomic number as the element, but a different
An isotope contains the same number of neutrons as the non-radioactive parent element. True
U-238 and U-235 are two naturally occurring isotopes of ____________________.
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 ___________.
The daughter of the U-235/Pb-207 isotope system is ___________.
The time that it takes a given amount of a radioactive isotope to be reduced by one-half is called
the isotopes ____________.
What is the name of the constant that reflects the rate at which a radioactive isotope decays per
unit of time?
The number of parent isotopes remaining at time t is what parameter in the equation N = No(e-
What is in the equation N = No(e-t)?
Given 100 atoms of an isotope, how many will be left after one half-life?
Given 100 atoms of an isotope, how many will be left after three half-lives?
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])?
What isotope system would you use to date a very young rock?
What isotope system would you use to date a Pleistocene tree trunk?
What isotope system would you use to date volcanic deposits containing a dinosaur?
Of the isotopic systems mentioned in this chapter which has the longest half-life?
Of the isotopic systems mentioned in this module which has the smallest half-life?
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?
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
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.