Earthtime

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.