At the time Darwin’s On the Origin of Species was published, the earth was “scientifically” determined to be 100 million years old. In 1947, geologists firmly established that the earth was 3.4 billion years old.Finally in 1976, they discovered that the earth is “really” 4.6 billion years old.All three of these decay processes have half-lives measured in billions of years.
This extrapolation is based on the fact that an unstable (radioactive) chemical element, called the parent isotope, breaks down at a presently known rate to form a more stable daughter isotope.
Evolution, depending as it does on pure chance, requires an immense amount of time to stumble upon anything remotely approaching the integrated complexity we see in even the simplest living things.
Much of the controversy between evolutionists and creationists concerns the age of the earth and its fossils.
To date a specimen by radiometric means, one must first know the starting amount of the parent isotope at the beginning of the specimen’s existence.
Second, one must be certain that there were no daughter isotopes present in the beginning.