Radioactive decay and dating rocks
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
In alpha decay, the nucleus ejects a helium nucleus (alpha particle) composed of two neutrons and two protons, dropping the mass of the original nucleus by four mass units.
(These include the variety of elements used in ‘standard’ radioisotope dating, mature uranium radiohalos and fission track dating.) It would be hard to imagine that geologic processes alone could explain all these.
Rather, there was likely to be an answer that concerned the nuclear decay processes themselves.
The first lesson, Isotopes of Pennies, introduces the idea of isotopes.
The final lesson, Frosty the Snowman Meets His Demise: An Analogy to Carbon Dating, is based on gathering evidence in the present and extrapolating it to the past.