Absolute Agex - Groverworld

sadhospitalMécanique

22 févr. 2014 (il y a 3 années et 7 mois)

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Absolute Age

Attempts at Absolute Age


Became more important in the age of Darwin.


Rate of Sedimentation


If the rate was constant over time, then we could
tell how old rocks are by their thickness

Radioactivity


Isotopes


elements
with different mass
number (different
number of Neutrons)


These Isotopes break
down over time

Radioactive Decay


Release of particles from the nucleus


This decay happens in a predictable way for
each element

Rates of Decay


Half Life
-

time required for half of the
radioactive isotope to decay.


Rate of decay are unchanged by environmental
conditions


This allows them to be a reliable source for dating

Radio

Active Element

Half Life

Carbon 14

5730 yrs

Uranium 238

4.5 billion years

Potassium
-
40

1.3 billion

years

The Rock Clock


Radiometric Dating


use of radioactive
decay to date rock
ages


Based on the
amount of
radioactive material
left in a rock

The math of radiometric dating

What percentage of a
radioactive element
would you have left
after 1 half life?


50%

What about 2 half lives?


25%

What about 3 half lives?


12.5%