Figure 4.

(a) The relationship between the fractional turnover in hiatus-bound sediment packages and percentage genera extinctions within geological stages (data from Heim & Peters [26]). Points more recent than the Early Ordovician are denoted in red, illustrating that extinctions of genera and hiatuses in marine packages are well-correlated. This correlation suggests that the fractional loss of genera during an extinction pulse may be related to lithological changes. (b) We propose several modern analogies to sedimentary hiatuses that may provide constraints for the current crisis. Specifically, the x-axis, mass extinction debt, is the percentage of genera that will go extinct if no efforts are made to return sedimentary processes to a pre-human state. In red on the y-axis is the per cent habitat destruction, linked via a species–area relationship. The left axis, in blue, is the equivalent lithological change resulting from the habitat loss. We propose that quantifying the relationship between the right and left axes serves as the most direct comparison to geological extinction events. (Online version in colour.)