Morphological Biosignatures and the Search for Life on Mars

This report provides a rationale for the advances in instrumentation and understanding needed to assess claims of ancient and extraterrestrial life made on the basis of morphologi-cal biosignatures. Morphological biosignatures consist of bona fide microbial fossils as well as microbially influenced sedimentary structures. To be recognized as evidence of life, mi-crobial fossils must contain chemical and structural attributes uniquely indicative of micro-bial cells or cellular or extracellular processes. When combined with various research strate-gies, high-resolution instruments can reveal such attributes and elucidate how morphological fossils form and become altered, thereby improving the ability to recognize them in the ge-ological record on Earth or other planets. Also, before fossilized microbially influenced sed-imentary structures can provide evidence of life, criteria to distinguish their biogenic from non-biogenic attributes must be established. This topic can be advanced by developing process-based models. A database of images and spectroscopic data that distinguish the suite of bona fide morphological biosignatures from their abiotic mimics will avoid detection of false-positives for life. The use of high-resolution imaging and spectroscopic instruments, in conjunction with an improved knowledge base of the attributes that demonstrate life, will maximize our ability to recognize and assess the biogenicity of extraterrestrial and ancient terrestrial life. Key Words: Biosignatures—Morphological fossils—Microfossils—Stromato-lites—Extraterrestrial life—Biogenicity—Paleobiology. Astrobiology 3, 351–368