Transcript Absolute_Age_Dating

Absolute Age Dating
Telling Geologic Time
Radioactive Decay
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Some elements are radioactive (unstable)
and decay as a result
These elements can be found in igneous &
met. rocks
We measure the time they take to decay
One element will become another element
as the atom loses protons
This is RADIOACTIVE DECAY
Parent - Daughter Material
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The radioactive element is the PARENT
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The stable element it turns into the DAUGHTER
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Radiometric Dating: calculating the age by comparing
the amount of parent to daughter material remains
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Half-life: refers to the time it takes for half of the parent to decay
Order of
Decay
Carbon-14
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Used only for organic remains
Accurate only back to about ~75,000yrs
Its half-life is 5700yrs
Tree Rings
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Dendrochronology: study of annual tree rings
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Trees grow unevenly during the year
Grow faster in the summer (fatter rings) than the winter
(thinner rings)
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2 sets of rings = 1 year
Iridium Layer
Chicxulub impact crater
What wiped out the dinosaurs?
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The impact blasted rock debris into the
atmosphere spreading a thin layer of iridium
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This layer acts as a marker to the end of the
Mesozoic (age of the dinosaurs) and the beginning of
the Cenozoic (age of the mammals)
Climate Records - Varves
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During the latest glaciation (Ice Age), ice would partially
melt during summer
Deposits carried into lakes by streams were light colored
Winter deposits are dark colored
These act like tree rings and record seasons