New Mexico Geological Society Annual Spring Meeting — Abstracts

How long can microorganisms remain viable in sediments, fluid inclusions, rock fractures, ice, or other geological materials? This is a question for which we have little direct evidence, but great interest. Reports of long duration microbial survival in salt crystals and other materials have been greeted with skepticism because the standards of proof are so rigorous and materials like salt are subject to plastic deformation and flow over geological time. Any hint of surface contamination undermines the ability to claim that recovered organisms are indeed survivors from past environments. However, as such instances slowly mount up in the scientific literature, the plausibility, indeed probability, of extremely long term survival and viability is strengthened.

Our recent work on living microorganisms and sequenceable DNA from fluid inclusions in enormous selenite crystals, Fe oxide and clay rich wall material, and black solid inclusions in crystals in a high temperature cave environment is a new entry in the list of potential long-term survival of microorganisms in geological time capsules. Over 30 mixed cultures have been retrieved from these materials in several caves intersected by mining activities in Naica, Chihuahua, Mexico. These cave chambers were drained of hot (>50° C) hydrothermal water during mining of zinc, lead, minor silver and copper, thus allowing access to the chambers about a decade ago. Growth rates of the crystals and their maximum age (~500 ky) has been estimated. Using these values, we estimate the age of the fluid inclusions we sampled at approximately 50 ky old.

The Chihuahuan Desert environment of Naica is similar to that in the Chihuahuan Desert of New Mexico in terms of both climate and vegetation type and there are some broad similarities in various geological features. In the case of the Naica system, a large magma body ascending from great depth served to fracture the parent limestone. Ascending metal rich thermal waters and gases percolated into the fractures, creating the caves and the ores, and setting the stage for the spectacular mineralogical developments and unusual microbial communities. This is an extraordinary example of the dramatic geochemical and biological influences that mantle-derived materials can ultimately have on shallower geology and microbiology.