There have been a lot of refinements since 1975 but, the Hadean period and the great bombardmenr, while difficult to document due the scarcity of geological evidence, goes to your point. However the discoveries in plate tectonics and greater understanding of relationships among the core, mantle and crust have revised our understanding of when and how the cooling will progress. In short, there are plenty of processes keeping the heat on. Without them, we would already be like Mars. Studies like this go back a couple of billion years and find incremental changes.
Thanks. Isn’t the heat in the earth’s core resulting from radioactive element decay?
Fascinating!!!