GEO 1111 Lecture Notes - Lecture 7: Closure Temperature, Geologic Time Scale, Radiocarbon Dating
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14 Aug 2016
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Why is partial melting a key term?
Some minerals melt and other stay intact
Partial melting the mantle (ultra mafic): oceanic crust (mafic)
Geological time scale (continued)
Absolute dating
Radiometric dating: uses half-life of radioactive isotopes, measuring
parent vs. daughter isotope ratios, therefore, constrains time (like
watching popcorn pop, kernels “parent” decrease and popcorn “daughter”
increases)=
Half life: the time it takes for half of the parent isotope to decay into
daughter isotopes
Uranium used to date materials that are millions of year sold
Carbon used to date more recent materials
Below certain temp., isotopes will no longer disuse in and out, and the
minerals radiometric clock starts (closure temperature)
Radiometric dating provides the time at which the rock crystallized, last
cooled down below the closure temperature
Radiocarbon dating: wood or shells are most suitable, the 14C clock begins
when the organism dies
Steps:
oCollect sample
oBurn it to release CO2
oMeasure beta emissions from CO2 in a steel-plated Geiger
oUse known decay rate curve to obtain 14C age
Absolute dates help infer how fast events in the various spheres occur,
such at the colonization of Polynesia
Measuring carbon dating of items (organic) in layers above and below the
target (inorganic) can helps give a range of age
Radiometric dating requires 10 half-lives, 14C is no good for that
Eras
Paleozoic: old life
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