6 rules relative age dating
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.
Principle of cross-cutting relations: Any geologic feature is younger than anything else that it cuts across.
Some elements have forms (called isotopes) with unstable atomic nuclei that have a tendency to change, or decay.
This happens at any time when addition of the fleeting "weak nuclear force" to the ever-present electrostatic repulsion exceeds the binding energy required to hold the nucleus together.
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.
This is a stable condition, and there are no more changes in the atomic nucleus.
A nucleus with that number of protons is called lead (chemical symbol Pb). This particular form (isotope) of lead is called Pb-207.
But if there are too many neutrons, the nucleus is potentially unstable and decay may be triggered.
Where the amounts of parent and daughter isotopes can be accurately measured, the ratio can be used to determine how old the rock is, as shown in the following activities.
Part 2a Activity At any moment there is a small chance that each of the nuclei of U-235 will suddenly decay.
Students should be able to understand the principles and have that as a background so that age determinations by paleontologists and geologists don't seem like black magic. Geologists in the late 18th and early 19th century studied rock layers and the fossils in them to determine relative age.
William Smith was one of the most important scientists from this time who helped to develop knowledge of the succession of different fossils by studying their distribution through the sequence of sedimentary rocks in southern England.