Part of our ability to date the rock sequences we see in the world and determine which are older and which younger has to do with simple observation. We see that older rocks contain trilobites and a wee bit above those we see ammonites, then clams and oysters in newer sediments. For a long time, this simple observation held us in good stead. We had a relative timescale for the Earth and this allowed us to piece together the biologic and geologic picture much clearer.
To understand and date rock in absolute terms required advances in science, in chemistry in particular, that we achieved in large part by 1895. This was the beginning of our understanding of distinct elements and the periodic table of elements. To many, the table is a memory of science classes from our youth and long forgotten. But in the period table, we find both the tremendous history of human achievement and the aha moments that help us to understand simple yet complex concepts like radioisotope decay — the genius tool we use for the absolute dating of rocks and fossils.
To that end, I highly recommend Sam Kean's book, The Disappearing Spoon. It is a tasty romp through madness, love and the history of the world through the eyes of the periodic table. You may find that within the stories that the table becomes more real for you and that the mysteries it holds are more easily within your grasp.