
_{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 nonradioactive parent element. True
or false}
false

_{U238 and U235 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 U238/Pb206 isotope system is ___________.}
U238

_{The daughter of the U235/Pb207 isotope system is ___________.}
Pb207

_{The time that it takes a given amount of a radioactive isotope to be reduced by onehalf is called
the isotopes ____________.}
halflife

_{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(et)?}
decay constant

_{Given 100 atoms of an isotope, how many will be left after one halflife?}
50

_{Given 100 atoms of an isotope, how many will be left after three halflives?}
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?}
C14/N14

_{What isotope system would you use to date a Pleistocene tree trunk?}
C14/N14

_{What isotope system would you use to date volcanic deposits containing a dinosaur?}
K40/Ar40

_{Of the isotopic systems mentioned in this chapter which has the longest halflife?}
Rb87/Sr87

_{Of the isotopic systems mentioned in this module which has the smallest halflife?}
C14/N14

_{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 UPb method.

_{Minerals such as Kfeldspar, biotite, and hornblende all contain the element K. What isotopic
system would you use to date these minerals?}
_{K40/Ar40}

_{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, UPb

_{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.

