The region is fractured and is likely volcanic in origin. Biogenic Living microorganisms, such as methanogens, are another possible source, but no evidence for the presence of such organisms has been found on Mars. In Earth's oceans, biological methane production tends to be accompanied by ethane () generation. The long-term ground-based spectroscopic observation did not find these organic molecules in the Martian atmosphere. Given the expected long lifetimes for some of these molecules, emission of biogenic organics seems to be extremely rare or currently non-existent. The reduction of carbon dioxide into methane by reaction with hydrogen can be expressed as follows: CO2 + 4 H2 -> CH4 + 2 H2O (∆G˚' = -134 kJ/mol CH4) This reaction of CO2 with the hydrogen to produce methane is coupled with the generation of an electrochemical gradient across the cell membrane, which is used to generate ATP through chemiosmosis. In contrast, plants and algae obtain their energy from sunlight or nutrients. Measuring the ratio of hydrogen and methane levels on Mars may help determine the likelihood of life on Mars. A low H2/CH4 ratio in the atmosphere (less than approximately 40) may indicate that a large part of atmospheric methane could be attributed to biological activities, but the observed ratios in the lower Martian atmosphere were "approximately 10 times" higher "suggesting that biological processes may not be responsible for the observed CH4". Since the 2003 discovery of methane in the atmosphere, some scientists have been designing models and in vitro experiments testing the growth of methanogenic bacteria on simulated Martian soil, where all four methanogen strains tested produced substantial levels of methane, even in the presence of 1.0 wt% perchlorate salt. Methanogens do not require oxygen or organic nutrients, are non-photosynthetic, use hydrogen as their energy source, and carbon dioxide (CO2) as their carbon source, so they could exist in subsurface environments on Mars. If microscopic Martian life is producing the methane, it probably resides far below the surface, where it is still warm enough for liquid water to exist. Research at the University of Arkansas published in 2015 suggested that some methanogens could survive on Mars' low pressure in an environment similar to a subsurface liquid aquifer on Mars. The four species tested were Methanothermobacter wolfeii, Methanosarcina barkeri, Methanobacterium formicicum, and Methanococcus maripaludis. A team led by Gilbert Levin suggested that both phenomena—methane production and degradation—could be accounted for by an ecology