Did Earthquakes Keep the Early Crust Habitable?

Abstract

The shallow habitable region of cratonal crust deforms with a strain rate on the order of ∼10⁻¹⁹ s⁻¹. 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 ∼10⁻¹⁵ 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.