|Gas bubbles out through water in|
the bottom of a deep mine in Timmons, Ontario, This image
is from the CNN blog site found here.
While the CNN blog (referred to in the figure caption) plays up the implications for ancient life (none has yet been found in this water) and hence ancient life on Mars hidden in deep old pockets of water, the Nature article** is of interest for other reasons. The abstract points out that old fluids are generally studied in very small amounts--as fluids, called "fluid inclusions," trapped in crystals at the time of growth of the crystal. Until this paper, ancient fluids have not been found outside of these inclusions, for example on the surfaces of minerals at their interfaces, or in fractures in the rock. As the crust deforms throughout geologic time, these fluids move around and come to be preserved in pockets. In one system 2.8 km below the surface in a gold mine in South Africa, fluids that are several tens of millions of years old contain "extant chemoautotrophic microbes". What does that mouthful mean? "Extant" means "still surviving," and "chemoautotrophic" means that these organisms obtain their energy from chemical reactions such as hydrogen sulfide, sulfur, ferrous iron, molecular hydrogen, and ammonia, and that they use CO2 for the carbon to make organic molecules. Bacteria and archaea that live in hostile environments such as deep sea vents are often chemoautotropes.
The authors of the article sampled fluids 2.4 km below the surface in crystalline rocks that are about 2.7 billion years in age. The Timmins mine is in a massive sulphide deposit producing copper and zinc ores. The fluids sampled discharge from exploration boreholes that have flow rates of 0.1 to over 2 liters per minute. Xenon and radiogenic noble-gases in these fluids provide evidence that these fluids have been isolated for at least a billion years, and possibly as long as 2.64 billion years. While they have not (yet, at least) found evidence for life in these fluids, the paper stresses that the fluids are of a composition capable of supporting life, and that the fact that they can be isolated in the earth's crust for these long times "may require changes in our understanding of the extent of the Earth's crust that may be habitable." By analogy, the authors speculate that similar fluids could be in the tectonically quiet geologic terrains on Mars for similar periods of time.
**Holland, G., and others, "Deep fracture fluids isolated in the crust since the Precambrian era," Nature, 497, 16 May 2013, page 357.