An Atacama subsurface tephra layer reveals how life colonized Kenorland in the Neoarchean.

Much has been published on the microbiology of the Atacama Desert, the driest and oldest place on Earth, but little is known about how microbial life is able to permanently colonize this extremely harsh environment. Given that wind transports vast amounts of viable microbial cells from the Pacific Ocean across the entire Atacama on a daily basis, it is difficult to identify the true native microbial inhabitants from recent arrivals. Here, we present a unique site-Mancha Blanca-located at the western edge of the Coastal Range of this desert. Containing a Miocene tephra subsurface layer, this site's unique differential habitability unveils the fate of new arrivals, and thus, the identity and metabolic strategies of the species that are eventually able to adapt and become some of the true inhabitants of the Atacama. Our findings show that the extreme conditions of the Atacama stochastically select for species arriving from the Pacific Ocean that already possess the molecular mechanisms needed to tolerate salinity, and thus are capable of inhabiting the driest desert on Earth. The colonization processes still detectable in the regions studied allow us to suggest the mechanistic and evolutionary pathways that may have been involved in the colonization of Kenorland by microbial life from the Panthalassic Ocean during the Neoarchaean. We propose the Coastal Range/hyperarid core of the Atacama as a model system for understanding the colonization of land 2.6 billion years ago.