Quantification of geological time represents one of the fundamental challenges for earth
scientists as it permits the determination of rates of change, integration of disparate geological
datasets and assessment of coincidence (or lack thereof) so often central to hypothesis
testing. Knowing the age of certain rocks, be it a thick accumulation of volcanic lava or an
extinction layer, allows us to say something about causality. The extinction of the dinosaurs
at the end of the Cretaceous Period, ‘about’ 66 million years ago is the poster child for such
cause-and-effect arguments. At ‘about’ the same time, a large asteroid struck what is now the
Gulf of Mexico, however a series of voluminous volcanic eruptions in India are also ‘about’ the
same age. Both are viable kill mechanisms, and both are closely correlated in time with the
extinction, but knowing they are ‘about’ the same age is not good enough
