Astrobiology December 2007, 7(6): 1023-1032
The shallow habitable region of cratonal crust deforms with a strain rate on the order of 1019 s1. This is rapid enough that small seismic events are expected on one-kilometer spatial scales and one-million-year timescales. Rock faulting has the potential to release batches of biological substrate, such as dissolved H2, permitting transient blooms.
In addition, the steady-state deformation of the brittle crust causes numerous small faults to be permeable enough (on the order of 1015 m2) for water to flow on a kilometer scale over relatively short geological times (105 yr). Hence, active faults act as concentrated niches capable of episodically tapping resources in the bulk volume of the rock. Radiolysis and ferrous iron are potentially bases of sustainable hard-rock niches.