Relative age dating of rocks activity
U-235 is the parent isotope of Pb-207, which is the daughter isotope.Many rocks contain small amounts of unstable isotopes and the daughter isotopes into which they decay.On a piece of notebook paper, each piece should be placed with the printed M facing down. The candy should be poured into a container large enough for them to bounce around freely, it should be shaken thoroughly, then poured back onto the paper so that it is spread out instead of making a pile.This first time of shaking represents one half life, and all those pieces of candy that have the printed M facing up represent a change to the daughter isotope.Some half lives are several billion years long, and others are as short as a ten-thousandth of a second.Return to top A tasty way for students to understand about half life is to give each team 100 pieces of "regular" M & M candy.Principle of cross-cutting relations: Any geologic feature is younger than anything else that it cuts across.
Very careful measurements in laboratories, made on VERY LARGE numbers of U-235 atoms, have shown that each of the atoms has a chance of decaying during about 704,000,000 years.
If the nucleus has not yet decayed, there is always that same, slight chance that it will change in the near future.
Atomic nuclei are held together by an attraction between the large nuclear particles (protons and neutrons) that is known as the "strong nuclear force", which must exceed the electrostatic repulsion between the protons within the nucleus.
That chance of decay is very small, but it is always present and it never changes.
In other words, the nuclei do not "wear out" or get "tired".
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For example, U-235 is an unstable isotope of uranium that has 92 protons and 143 neutrons in the nucl eus of each atom.