![]() In particular, erosion of gypsum deposits provides the groundwater with sulfate levels that are 100 times higher than Lake Huron water. These geochemicals are picked up as groundwater slowly dissolves the limestone, dolomite, and gypsum bedrock - also known as marine evaporite layers. Higher level of ions is also indicated by the higher conductivity measured in the groundwater. The groundwater also had lower redox potential, pH, dissolved organic carbon, and nitrate levels, and higher dissolved inorganic carbon, chloride and carbonate ions. The temperature of the venting groundwater keeps the sinkhole's floor at a stable and cool 9 oC. Many microbes and higher organisms need oxygen for their survival, so the submerged sinkholes sustained by groundwater are an extremely different habitat when compared to normal lakes. We found two important clues: venting groundwater contained no oxygen, but had high levels of the element sulfur, measured in the form of sulfates (Table 1, Figure 3b). What are the characteristics of the venting groundwater that nurture extensive microbial growth (Figure 1)? To answer this question, we gathered data using a variety of water quality sensors, and collected samples of lakewater and groundwater for laboratory analyses. Explorations using research vessels, remotely operated vehicles (ROVs), scuba divers, underwater sensors, metabolic chambers, sediment corers, as well as laboratory-based studies are revealing a fascinating working picture of this unique ecosystem (Biddanda et al. Since 2002, scientists interested in the geology, hydrology, chemistry and biology of sinkholes have explored these habitats. Here, colorful microbial mats with bubbling gasses have been discovered which are not found anywhere else in the Great Lakes, and are known to occur in just a few other places on Earth. The sinkholes' inhabitants - mostly microbes - are providing us a glimpse of what early life on Earth might have been like and how it might have transformed the planet. Well, scientists have discovered such a place within collapsed depressions along the lake floor in what are called submerged sinkholes in Lake Huron, one of the five Great Lakes located in North America. Imagine being able to look back into the distant past through a "time-portal." Wouldn't it be fascinating to see life as it was 2.5 billion years ago (bya) in the shallow seas of the early Earth? These were harsh times when there was no available oxygen, and life was entirely composed of microorganisms.
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