Morphological Biosignatures and the Search for Life on Mars

Abstract

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 morphological biosignatures. Morphological biosignatures consist of bona fide microbial fossils as well as microbially influenced sedimentary structures. To be recognized as evidence of life, microbial fossils must contain chemical and structural attributes uniquely indicative of microbial cells or cellular or extracellular processes. When combined with various research strategies, 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 geological record on Earth or other planets. Also, before fossilized microbially influenced sedimentary 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.

Development and evaluation of a microdevice for amino acid biomarker detection and analysis on Mars

“…Furthermore, the debate over the origin of magnetite and polyaromatic hydrocarbons in the ALH84001 meteorite (22)(23)(24) illustrates that unambiguous biomarkers must be agreed on and analyzed in situ. Although different approaches have been proposed (25), amino acids are uniquely useful biomarkers in the search for extinct or extant life because they are critical components of terrestrial life and their enantiomeric ratios can be used to determine their origins. The MOA developed here exploits the most modern lab-on-a-chip technologies to achieve the goal of highly sensitive amino acid biomarker detection and to demonstrate analyses of relevant samples from the Atacama Desert, Chile, and in the Panoche Valley, CA.…”

A fresh look at the fossil evidence for early Archaean cellular life

“…Cady et al 2003;Brasier et al 2005 and references therein). This can be tested by laser Raman spectra (Pasteris & Wopenka 2002) or atomic force microscopy (Altermann & Kazmierczak 2003), though both need to be coupled with careful contextural and petrographic mapping to falsify the 'null hypothesis' of an abiogenic origin (Brasier et al 2002; see also Schopf et al 2002;Tice & Lowe 2004).…”

New insight into the origin of manganese oxide ore deposits in the Appalachian Valley and Ridge of northeastern Tennessee and northern Virginia, USA

“…Clays have also been shown to act as nucleation surfaces for modern Mn and Fe oxides (Xu and Lee, in press). There are notable similarities in morphology of these ores to those produced in modern biomineralizing environments, such as hot springs in Yellowstone National Park (Cady et al, 2003;Lowe and Braunstein, 2003;Parenteau and Cady, 2010;Smythe, 2015) and in living biofilms on Satsuma-Iwo Jima, a volcanic island in Japan (Tazaki, 2000). The small size (< 1 µm) of many of the encrusted filaments and sheets suggests that extracellular polymeric substances (EPS) as well as cell surfaces and clay particles may have acted as nucleation sites.…”