Microorganisms are intimately linked to minerals on Earth due to their ubiquitous distribution, their metabolic diversity and their highly reactive nature. Microorganisms are ubiquitous on Earth today and are found in all locations were liquid water is present. Microorganisms are also highly diverse, having evolved numerous metabolic strategies to take advantage of various energy and carbon sources available on Earth. Finally, their high surface to volume ratio means microbial cells and extracellular products act as highly reactive interfaces. This combination leads to their ability to interact with their environment in ways that can influence geological processes such as mineral precipitation, rock weathering and even ore body formation. Microorganisms can thus act as geological agents, transforming the Earth and its constituents. This intimate relationship has existed for well over 3 billion years, since the earliest known microorganisms on Earth. However, microorganisms are rarely well preserved in ancient geological materials. Instead, they commonly leave physical, chemical and isotopic traces, or biomarkers, in minerals and rocks. These biomarkers provide clues about the nature and activity of past microbial life.|
On Mars, abundant microbial life could have existed in the past, when it was a warmer and wetter planet. If this were the case, microbial biomarkers would likely be present in ancient sedimentary deposits, such as in clays or sulphate minerals, as have been recently discovered by orbiters and rovers. In order to eventually assess the possibility of ancient life on Mars, it is therefore essential to understand in greater detail the linkages between microbiology and mineralogy, especially in the context of Martian geology. This can best be accomplished by studying analog environments on Earth, by developing culture-based experiments and by using molecular tools (both mineralogical and microbiological) to probe the microbial-mineral interface.