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Through their space missions and astronomical observations of other worlds, NASA's programs of exploration are uniquely positioned to contribute to a fundamental understanding of the origins, evolution and distribution of life in the universe. We are emboldened in our cosmic search for life by recent observations that our own biosphere began perhaps quite soon after Earth's formation, that liquid water once existed on Mars and Europa, and that planetary systems might indeed be common in the universe. Our search must proceed by first identifying the distribution of life-sustaining environments in our solar system and beyond, and then by learning how to detect evidence of life in the context of geologically-active, habitable planets.
Our one and only model of life in the universe is life on Earth, and life on Earth is overwhelmingly dominated by microbial life, both in terms of biomass and the amount of time present on Earth. In fact, eighty percent of the entire history of life on Earth is the history of exclusively microbial life. Microbes have a lot to teach us about successful strategies for staying alive on geologically active planets over extremely long periods of time.
Microbial mats are important because their 3.4-billion-year fossil record indicates that they are the Earth's oldest known ecosystems. Photosynthetic microbial mats are key because, today, sunlight powers more than 99 percent of global primary productivity. For most of Earth's history, photosynthetic ecosystems have affected the atmosphere profoundly and have created the most pervasive, easily-detected fossils. Therefore, surface-dwelling biospheres on other planets that derived their energy principally from sunlight will be the ones most amenable to detection via telescopes or spacecraft.
Microbial mat research is specifically relevant to four key aspects of Astrobiology (named as goals in NASA's Astrobiology Roadmap). These four aspects are as follows:
1. Relevance to the study of Life on Earth
In order to understand the early evolution of our own biosphere, we must study "two natural repositories of evolutionary history available on Earth: the molecular record in living organisms and the geological record in rocks" (NASA Research Announcement NRA 97-OSS-11). This is articulated in Astrobiology Roadmap as Goal 3 "Explore How Life Evolves on the Molecular, Organism, and Ecosystem Levels". Stromatolites, which are fossilized microbial mats, are the oldest and most pervasive evidence of life on Earth. For many of the environments where mats are found today, fossil stromatolites can also be found. For a few examples from this fossil record, click here.
2. Relevance to the study of the co-evolution of life and Earth
Our own biosphere has been a "geobiological agent" that has both modified and adapted to Earth's changing environment. For most of Earth history, life was limited to microbes. To understand our own origins and to recognize life elsewhere, we must learn more about the processes of co-evolution of our own early microbial biosphere and its environment. Studies of microbial ecosystems are paramount because the evolution and survival of the early biosphere depended upon the efficient coordination of resources and processes by diverse microbial populations. This is articulated in NASAs Astrobiology Roadmap as Goal 4 "Determine How the Terrestrial Biosphere has Co-evolved with the Earth".
3. Relevance to the study of the possibility of life elsewhere
Microbial mats on Earth may be key in our attempts to identify and recognize life elsewhere in the solar systems. This goal is articulated in NASA's Astrobiology Roadmap as Goal 8: "Determine whether There Is (or Once Was) Life Elsewhere in Our Solar System, Particularly on Mars and Europa". We must learn how to interpret better the "biological marker" features, or "biomarkers," that might occur in samples returned from Mars and elsewhere. Working with biomarkers produced on our own planet (for which we also have other types of fossils) is an important step in searching for biomarkers elsewhere. The need for such biomarker research has been highlighted convincingly by the recent controversies regarding claims of Martian "biomarkers" in the meteorite ALH84001.
4. Finding life outside our own solar system
Our ability to identify both life-sustaining environments and biospheres beyond our own solar system depends upon our ability to interpret infrared spectra of distant planetary atmospheres for possible contributions from geological processes and biospheres (Terrestrial Planet Finder web site). NASA has recognized the importance of this search in Goal 7 of the Astrobiology Roadmap "Determine How to Recognize the Signature of Life on Other Worlds". On Earth, we can study the production of these important trace gases by communities of microorganisms known to have been present on Earth for over 3.5 billion years.
Our research group specifically addresses certain key aspects of microbial mats that are relevant to NASA's objectives. Much of early biological evolution took place in microbial mat communities, therefore we must understand the structure and function of the mat microenvironment, which is, after all, the actual environment experienced by the individual microbe. Microbial mats harbor an extraordinary biological diversity that we are just beginning to discover, let alone understand.
Our group acronym (EMERG) is also a reference to our approach. Microbial communities have "emergent properties" that would not necessarily be expected or predicted from the study of the individual microorganisms present in the community. The products of microbial ecosystems, namely the chemical species and sedimentary textures that impact the atmosphere or leave remains in sediments, are examples of emergent properties of these ecosystems. The nature of these gaseous products and fossil biomarkers are created through the ecological interactions of the community members. In order to begin to understand these emergent properties, what is needed is a multidisciplinary team, studying the ecosystem as a whole. Further, to learn most effectively how to understand lifes impact upon its environment and to interpret the early fossil record, we must understand the structure and function of microbial mat communities under both modern conditions and conditions that mimic Earths early environments.
|Page 1||What are Microbial Mats?|
|Page 2||What are Stromatolites?|
|Page 3||Interactive Gallery|
|Page 4||Why is NASA Interested in Microbial Mats?|
|Page 5||How do Microbial Mats Work?|
|Page 6||Microbial Mat Research at NASA Ames Research Center|
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