Fossil record dating assumptions
Relative dating does not provide actual numerical dates for the rocks.Fossils are important for working out the relative ages of sedimentary rocks.Harlow Shapley, who wrote an article in 1919 on the subject, was an astronomer, responsible for the detection of the redshift in distant nebulae and hence, indirectly, for our present concept of an expanding universe. Russell, author of the 1921 article on radioactive dating, was familiar to me for his part in developing the Hetzsprung-Russell diagram for stars, but I was surprised to discover that he was also the Russell of Russell-Saunders coupling, important in atomic structure theory. The prologue to the drama is the mid-19th century recognition of the relation between heat and other kinds of energy (see the 1857 article “Source of the Sun’s Heat”).
That fossil species may have been dated somewhere else, so you can match them and say that your fossil has a similar age.
Radioactivity offered not only a resolution to the puzzle of the earth’s energy supply but also a chronology independent of questionable geologic assumptions and a depth of time more than adequate for the processes of evolution.
Lord Kelvin and his allies used three kinds of argument.
One outstanding feature of this drama is the role played by those who themselves were not, or not exclusively, geologists.
Most notable is William Thomson, ennobled to become Lord Kelvin in 1892, whose theories make up an entire section of this collection.