In the search for life on Mars or any planet, there is much more than the presence of carbon and oxygen to consider. Using Earth's biogeochemical cycles as a reference point, elements like nitrogen, iron and sulfur are just as important for supporting life. As explored in studies published in February's open-access Special Issue of Frontiers in Ecology and the Environment, the most basic elements work together to support an extraordinary diversity of life.
Cycles of carbon, nitrogen and phosphorous are intertwined and rely on organisms just as much as organisms rely on these elements, explains Edward Rastetter from the Marine Biological Laboratory in Woods Hole, Massachusetts, in one of the issue's articles. For instance, fallen leaves on a forest floor supply food for microbes which excrete nutrients back into the soil, benefitting nearby trees.
Microbes transform raw materials — such as chemicals, gases and sunlight — into biomass by a variety of metabolic processes. These energy-converting processes are as diverse as the microbes that conduct them, and are much more diverse than the metabolic capabilities of plants or animals, according to Amy Burgin from Wright State University in Dayton, Ohio, and colleagues in one of the issue's articles.