Atoms of the same element with differing atomic weights are called isotopes.
Radioactive decay is a spontaneous process in which an isotope (the parent) loses particles from its nucleus to form an isotope of a new element (the daughter).
With rare exception the taxonomic genus homo contains groups identified as true humans (as with Homo neanderthalensis, and Homo erectus), and those assigned to Australopithecus being true ape.
However, research by creationists has revealed a large number of problems with radiometric dating.
In some cases such as Carbon-14 dating, radioactive dating actually gives strong evidence for a young Earth, while other methods such as K-Ar dating and Isochron dating are based on faulty assumptions and are so unreliable as to be useless.
The next 40 years was a period of expanding research on the nature and behavior of atoms, leading to the development of nuclear fission and fusion as energy sources.
A byproduct of this atomic research has been the development and continuing refinement of the various methods and techniques used to measure the age of Earth materials. A chemical element consists of atoms with a specific number of protons in their nuclei but different atomic weights owing to variations in the number of neutrons.