Paleontology dating techniques
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.
In other words, during 704 million years, half the U-235 atoms that existed at the beginning of that time will decay to Pb-207. Many elements have some isotopes that are unstable, essentially because they have too many neutrons to be balanced by the number of protons in the nucleus.
Many rocks contain small amounts of unstable isotopes and the daughter isotopes into which they decay.
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.
Some very straightforward principles are used to determine the age of fossils.
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.
They are: Principle of superposition: Younger sedimentary rocks are deposited on top of older sedimentary rocks.
2) To familiarize students with the concept of half-life in radioactive decay.
In other words, the nuclei do not "wear out" or get "tired".
If the nucleus has not yet decayed, there is always that same, slight chance that it will change in the near future.
Through a series of changes within the nucleus, it emits several particles, ending up with 82 protons and 125 neutrons.
This is a stable condition, and there are no more changes in the atomic nucleus.
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Some elements have forms (called isotopes) with unstable atomic nuclei that have a tendency to change, or decay.