Abstract
As we expand the search for life beyond Earth, a water-dominated planet, we turn our eyes to other aquatic worlds. Microbial life found in Earth’s many extreme habitats are considered useful analogs to life forms we are likely to find in extraterrestrial bodies of water. Modern-day benthic microbial mats inhabiting the low-oxygen, high-sulfur submerged sinkholes of temperate Lake Huron (Michigan, USA) and microbialites inhabiting the shallow, high-carbonate waters of subtropical Laguna Bacalar (Yucatan Peninsula, Mexico) serve as potential working models for exploration of extraterrestrial life. In Lake Huron, delicate mats comprising motile filaments of purple-pigmented cyanobacteria capable of oxygenic and anoxygenic photosynthesis and pigment-free chemosynthetic sulfur-oxidizing bacteria lie atop soft, organic-rich sediments. In Laguna Bacalar, lithification by cyanobacteria forms massive carbonate reef structures along the shoreline. Herein, we document studies of these two distinct earthly microbial mat ecosystems and ponder how similar or modified methods of study (e.g., robotics) would be applicable to prospective mat worlds in other planets and their moons (e.g., subsurface Mars and under-ice oceans of Europa). Further studies of modern-day microbial mat and microbialite ecosystems can add to the knowledge of Earth’s biodiversity and guide the search for life in extraterrestrial hydrospheres.
Highlights
Introduction and BackgroundWhenever we look up at the night sky and wonder if there is life out there somewhere, our minds conjure images of water worlds, because life, as we know it, is water-based.Earth is a water-dominated planet located in the habitable, or “goldilocks”, zone around the Sun
A great variety of living microbial mats with a diversity of structural and functional characteristics are found in extant extreme ecosystems all over the world ranging from subglacial lakes to deep sea thermal vents [14]
Sulfur-rich environments inhabited by cyanobacteria, akin to those that were present long ago in Earth’s history, are found in the coastal waters of NW Lake Huron—a region underlain by karstic limestone wherein groundwater seeps through Paleozoic marine evaporites (Figures 1 and 2, Figures S1 and S2) [13]
Summary
Whenever we look up at the night sky and wonder if there is life out there somewhere, our minds conjure images of water worlds, because life, as we know it, is water-based. A great variety of living microbial mats with a diversity of structural and functional characteristics are found in extant extreme ecosystems all over the world ranging from subglacial lakes to deep sea thermal vents [14]. These extremophile microbial mats and their exceptional environments provide readily accessible and working scenarios that could assist us in better envisioning and exploring for life elsewhere in our solar system, such as in Mars, Enceladus, and Titan (Saturnian moons), and Ganymede and Europa (Jovian moons) [18]. We follow-up with a discussion regarding relevant aspects of how we have studied these ecosystems over the past two decades and scenarios of how these and additional approaches may be useful in studies of potential mat worlds encountered in other extraterrestrial bodies in the solar system
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