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© ELI, 2015

The deep terrestrial underground

Contrary to common perception, the deep subsurface is not one, massive, compressed space of rock. Rocks are fractured and in those fractures runs water. According to Gleick et al, 2010 only 0.3% of all fresh water is accounted for in rivers and lakes, 68.4 percent in glaciers and 30 percent resides underground making the underground freshwater reservoir 100 times bigger than on the surface. The age of the water can vary from a few thousand years to >2 billion years potentially holding biological clues of a very distant past on planet Earth. Archaea, bacteria and more complex multicellular organisms have been found as deep as >4 km underground in this fissure water, many never seen before and unique to this dark and hidden world devoid of any sunlight. Because this is an energy starved ecological niche, it is a demanding and harsh world for these organisms that have sometimes different metabolisms for utilizing e.g. naturally occuring radiation derived chemicals as an energy source. Some bacteria may only divide once every 1000 years because of the scarcity of energy in this system. The discovery in 2011 of a more complex multicellular nematode (’devilworm’) was as surprising as it was unexpected. This offers hope that on other planets with a harsh environment more complex lifeforms may be able to survive. Sampling on Earth can either be done by deep drilling or visiting the deepest mines in the world. Drilling has achieved greater depths but the samples are small. Deep mines (>4.5 km) allow one to sample thousands of liters of fissure water directly on the spot with more equipment. South Africa is the preferred country as it has not only many gold, diamond and platinum mines but because they are the deepest mines in the world today. It is the only place on the planet where one can walk and sample in excess of 4 km underground. During mining operations and exploratory drilling (hot) water filled fractures are hit, a nuisance to miners, but a bounty for scientists. Water fractures may be nothing more than dripping to gushing at tens of thousands of liters/hour. Typical analysis will consist of chemical composition of the water, isotope, gas and biological content. Specialised equipment and extreme care is taken to avoid any air/external contamination from spoiling these unique samples. In the laboratory all these samples are either studied in South Africa or sent and analysed in the laboratories of the international team of scientists from Belgium, USA, Canada, South Africa, England, Switzerland and Russia. By studying this hidden world where conditions are not all that different from some other planets or conditions on Earth long ago, we hope to gain insight into the processes, environments and adaptations that allow life to thrive in this realm. Based on preliminary calculations the biomass underground effectively dwarfs that of the surface, there is more in the deep underground than meets the eye.
All pictures copyright Eli except top right courtesy of Dr B.Linage Alvarez
The Science of ELi