Burial and Denudation Alter Microbial Life at the Bottom of the Hypo‐Critical Zone

Abstract

The Critical Zone (CZ), where water, rock and life interact (Brantley et al., 2006), may extend much deeper and contain much older groundwaters than is typically considered (e.g., a few tens of m and millions of years). Microbial communities are found in fluid-rock systems kilometers beneath the surface associated with millionto billion-year-old fluids (Magnabosco et al., 2018;Onstott et al., 2019). How these populations arrived at their current locations is largely unknown. Circulating meteoric waters extend to several kilometers driving fluidrock reactions and are certainly one potential source. Ancient microbial communities deposited with the rocks, or which migrated in previously, are likely to have experienced sterilization during periods of deep burial and