Strange life in stranger places
The drilling of the ocean floor and the earth’s crust for fossil fuels, minerals and research has led microbiologists to some surprising discoveries. Among these unexpected findings have been new forms of microscopic life, some of which live in sediments as much as a kilometer below the sea floor. Special techniques are used by the researchers to ensure that the micro-organisms they find are not the result of contamination of the drilling equipment used.
Surprisingly, the concentration of these organisms living deep in the 35 million year-old sediments was found to be as high as a million per cubic centimeter (or about 15 million per cubic inch). Many of the organisms present appear to thrive on methane (marsh gas) and sulfate and, where those nutrients were present in sufficient amounts, the concentration of organisms rose to as much as 10,000 times higher. In general though, there was little nutrient present and the question became how do these organisms metabolize and reproduce in such inhospitable environments? When the potential energy sources for these life forms were determined, it was calculated that it could take more than a thousand years for one of these cells to grow enough to divide into two daughter cells. Because such slow growth was not thought to be compatible with life, some believed these organisms were actually dead. However, further investigation showed them to be, indeed, alive. When their DNA was analyzed it showed that these strange organisms had no relatives among the well characterized bacteria that thrive on Earth’s surface or in the ocean. It is now estimated that, of the total mass of life on Earth, 30% lives below the ocean’s bottom.
Similarly, studies of microbes found living nearly 3 miles deep in the Earth’s crust uncovered a small variety of microorganisms living in rock fractures containing 3-25 million-year-old water. Among the potential nutrients found in this 140-degree+ Fahrenheit habitat, hydrogen and sulfate predominated. As there were no nutrients that might have been derived from photosynthesis, the conclusion was that hydrogen, produced by the natural radioactivity present in the rock, was used in energy yielding reactions to sustain the growth of these organisms. Some microbiologists have concluded that these crustal organisms also reproduce extremely slowly — just how slowly has yet to be determined.
Hotter yet is the environment near hydrothermal vents found near fractures in the ocean floor (these fractures occur where new ocean crust is being laid down by the upwelling of hot magma from below). Here, where temperatures up to 195 degrees Fahrenheit exist, a number of unusual creatures have been discovered and among them is a single-celled organism that produces methane and “fixes nitrogen.” This is the biologic process by which nitrogen from the air becomes incorporated into the nutrients necessary for most surface dwelling creatures. Prior to this finding, nitrogen-fixing had not been found to exist in organisms living at temperatures above 145 degrees F.
It is the existence of these many unexpected and remarkable forms of life that give hope to astrobiologists searching for life on other planets where the typical environment may be more extreme than most of Earth’s habitats.
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