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Geologic Time Part 2 (Exam 3)
Gary Girty GEO100-PLANET EARTH SDSU
20
Geology
Undergraduate 1
06/25/2010

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Term
Isotopic dating/Geochronology dating
Definition
Determining the ages of rocks through their contained radioactive element.
Term
Atomic mass
Definition
The isotope of a given element has the same atomic number as the element, but a different atomic mass.
Term
Uranium
Definition
U-238 and U-235 are two naturally occurring isotopes of uranium.
Term
Radioactive decay/radioactivity
Definition
The spontaneous disintegration of the nuclei of an atom.
Term
Half-life
Definition
The time that it takes a given amount of a radioactive isotope to be reduced by one half.
Term
Decay constant
Definition
The constant that reflects the rate at which a radioactive isotope decays per unit of time.
Term
N = No(e-/\t) for N
Definition
N is the number of parent isotopes remaining at time t.
Term
N = No(e-/\t) for N for /\
Definition
/\= decay constant
Term
Fundamental age equation or age equation
Definition
t = (1/ /\)(ln[(D/P)+1])
Term
t = (1/ /\)(ln[(D/P)+1]) for P
Definition
The amount of remaining original isotopic material
Term
C-14/N-14
Definition
Isotope system utilized to date very young rocks and a Pleistocene tree trunk.
Has the smallest half-life.
Term
K-40/Ar-40
Definition
Used to date volcanic deposits containing a dinosaur.
Used for minerals that contain element K.
Term
Rb-87/Sr-87
Definition
The isotopic system with the longest half-life
Term
What types of rocks are found at Jack Hills, NW Australia and why are they significant?
Definition
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.
Term
What isotopic system is used for minerals that contain element K?
Definition
K-40/Ar-40
Term
Isotopic system for crystal of zircon
Definition
U238/Pb260 or U235/Pb207
Term
What is the oldest Earth material and how old is it? Where is it?
Definition
Zircon, 4.4 b.y. Jack Hills, NW Australia.
Term
What, how old, and where is the oldest rock dated on Earth?
Definition
Acasta gneiss, 4.03 b.y., NW Canada.
Term
Can you date the age of the Earth from fossils?
Definition
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.
Term
What mineral and isotopic system were used to date the oldest detrital crystal and rock on planet Earth?
Definition
Zircon, U-Pb
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