http://www.amazon.com/The-Dating-Game-Search-Earth/dp/052189...

by Cherry Lewis [0].

It's an informative read. Especially the stuff about the actual calculations. It's fun to realise how massively the early approaches (salinity, heat transfer considerations, etc.) were blown out of the water by good old nuclear decay (Rubidium->Strontium, as I recall).

Once again, nuclear phenomena are damn near magical.

[0]: http://www.bris.ac.uk/earthsciences/people/cherry-l-lewis/in... . It's a solid department (though I'm biased - I used to study there). They're totally immersed in all things earth science. Rarely seen so much enthusiasm.