determination of the age of the earth (second method)

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Determination of the Age of the Earth (Second Method)

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Determination of the Age of the Earth (Second Method). Radioactivity in the Earth’s Crust. One can find the age of a rock by measuring the amount of radioactivity In particular one is interested in the daughter decay series K 40 half life (T 1/2 1277 million years) - PowerPoint PPT Presentation

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Page 1: Determination of the Age of the Earth (Second Method)

Determination of the Age of the Earth (Second Method)

Page 2: Determination of the Age of the Earth (Second Method)

Radioactivity in the Earth’s Crust• One can find the age of a rock by

measuring the amount of radioactivity

• In particular one is interested in the daughter decay series

• K40 half life (T1/2 1277 million years)

• Isotopic Abundance 0.118 %

• Age of earth about 4 billion years

Page 3: Determination of the Age of the Earth (Second Method)

Second Method Uranium and Actinium decay series

• U238 T1/2 = 4468 million years

• U235 T1/2 = 703.8 million years

• Both of these isotopes are not made in stars. They are “Transuranic Elements”

• Probably made during big bang and in Supernovae explosions

• Assume original abundance of these two isotopes were the same

Page 4: Determination of the Age of the Earth (Second Method)

Radioactive Decay

• Radioactive Decay is a logarithmic decay

teNN 0N is the number of atoms after a time t

N0 is the original number of atoms at time 0

is the decay constant

t is the elapsed time

= lne2 /T1/2 = 1/(1.44 T1/2) (Can be either years or seconds)

Page 5: Determination of the Age of the Earth (Second Method)
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