Miles below us, deep within Earth's crust, life is astir. Organisms there are not the large creatures typically envisioned when thinking of life. Instead, thriving there are microbes, the smallest and oldest form of life on Earth. Although the biological diversity of these deep biosphere microorganisms may surpass that of the more familiar surface biosphere, much about them is still unknown, including the origin of the organic compounds they consume. Arizona State University researchers are using a novel approach that integrates physical organic chemistry with organic geochemistry and biogeochemistry to uncover the source of these organic compounds.
Carbon, the building block of organic matter, is one of the most dynamic elements on the planet; it responds to biological, physical and chemical processes in many ways and on many timescales. Understanding how carbon is formed, where it comes from, and how much of it exists, is important for a more detailed and coherent picture of the global carbon cycle. Yet a complete understanding of how carbon is produced and consumed in the environment still evades researchers because much of what is known is based on processes that act on short time-scales and at Earth's surface.
Deep biosphere microbes, like any living organism, require energy to survive; for many, their sustenance comes in the form of organic compounds. Over time, organic compounds are buried and pushed deeper into the Earth's crust. Harsh conditions on the journey to the deep Earth cause the organic compounds to become "recalcitrant," meaning they are no longer in a form that microbes can use. Some of the consumable organic compounds are produced by other subsurface microbes, but a large portion is most likely the end product of a mysterious geochemical process.
Theoretical biogeochemist Everett Shock, a professor in ASU's School of Earth and Space Exploration and the Department of Chemistry and Biochemistry in the Colle
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Arizona State University