The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99%) and uranium-235 (which has 143 neutrons).
Uranium has the highest atomic weight of the primordially occurring elements.
Students not only want to know how old a fossil is, but they want to know how that age was determined.
Rather than study entire rocks and hope they date all the way back to the moon's birth, the team dated the formation of the object's mantle and overlying crust.
2) To familiarize students with the concept of half-life in radioactive decay.
3) To have students see that individual runs of statistical processes are less predictable than the average of many runs (or that runs with relatively small numbers involved are less dependable than runs with many numbers).
Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.
There are over forty such techniques, each using a different radioactive element or a different way of measuring them.