*5.1.2 Nodular/dendritic harder structures*

The harder structures may result from small grain aggregates, randomly dispersed, preferably along diverging alignments from scattered points. As a consequence, they assume several unusual shapes, forming lumps and nodules, and occasionally branched and/or overlapping bodies (called "dendritic"; [55]). The same structures also occur in the laminated sequences typically forming irregular crusts and emerging nodules, marked by an irregular scabrous surface, typical of stromatolites (known as "cerebrotic") and thrombolytic crusts. In these structures and on their surface, both in terrestrial and Martian samples, elongated and curved filaments are sometimes noted (**Figures 6** and **7**); most noteworthy, the elongated structures of Martian samples, occasionally exhibit regular septate forms (**Figures 6**–**9**).

**111**

**Figure 6.**

Such dendritic, nodular and laminate concretions have been investigated in detail by the NASA scientific team [52]. They found, comparable to the host rocks, notable Mg-enhancement and a strong depletion of other major elements; nickel also being reported by ChemCam. Since some sulfur was also detected in a dendritic feature, they interpreted the Mg occurrence as of the presence of MgSO4 phase; a

*from a laminated setting to a more chaotic structure (C), common for terrestrial microbialites.*

*These images show a series of filamentous/elongated microstructures taken by MAHLI (H,I) and ChemCham (A-B) in the hard concretion of the Murray Formation, in comparison to other Martian filamentous structures taken by Opportunity rover (G). The selected elongated microstructures (arrows and yellow circles are in relief in all frames); they show cross sections of 0.09–0.3 mm and regularly septate interspaces (more evident in G, H and I), forming elongated sinuous (D-I) and intertwined structures (E-I). On note the lateral discordance,* 

*Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531* *Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

#### **Figure 6.**

*These images show a series of filamentous/elongated microstructures taken by MAHLI (H,I) and ChemCham (A-B) in the hard concretion of the Murray Formation, in comparison to other Martian filamentous structures taken by Opportunity rover (G). The selected elongated microstructures (arrows and yellow circles are in relief in all frames); they show cross sections of 0.09–0.3 mm and regularly septate interspaces (more evident in G, H and I), forming elongated sinuous (D-I) and intertwined structures (E-I). On note the lateral discordance, from a laminated setting to a more chaotic structure (C), common for terrestrial microbialites.*

Such dendritic, nodular and laminate concretions have been investigated in detail by the NASA scientific team [52]. They found, comparable to the host rocks, notable Mg-enhancement and a strong depletion of other major elements; nickel also being reported by ChemCam. Since some sulfur was also detected in a dendritic feature, they interpreted the Mg occurrence as of the presence of MgSO4 phase; a

#### **Figure 7.**

*Harder septate filaments forming thin laminae (Murray Formation; Sols 1416–1418). Images show a series of filaments (as shown in sub-frames) having transverse dimension ranging from 50 to 150 microns. Such filaments stand out from the rock and show a sequence of aligned harder segments, having septate bodies. Their shapes are often sinuous, several millimeters long; in the above images they are in relief, orientated NW-SE, thus determining, due to their hardness, serrated contact between the laminae (white lines).*

**113**

**Figure 8.**

*transverse sections of conical bodies.*

*Morphological interpretation of some of the "rice grains" on an amplified MAHLI image (Sol 880). One can see repetitive curved (C), overlapping (O), fusiform (F), conical (Cn), very curved (VC), ring-shaped (R), curved/fusiform (C/F) shapes and therefore showing significant differences from the expected regular appearance of crystals. Note the presence of shapes (R and Cn types) which we have interpreted as possible* 

*Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

#### **Figure 8.**

*Morphological interpretation of some of the "rice grains" on an amplified MAHLI image (Sol 880). One can see repetitive curved (C), overlapping (O), fusiform (F), conical (Cn), very curved (VC), ring-shaped (R), curved/fusiform (C/F) shapes and therefore showing significant differences from the expected regular appearance of crystals. Note the presence of shapes (R and Cn types) which we have interpreted as possible transverse sections of conical bodies.*

#### **Figure 9.**

*Highlighting the most common forms observed in MAHLI images at Sols 809 and 880. The amplified image in the center shows the following types: elongated/curved body (1), occasionally septate (frame left on the top; see dashed line), lenticular/curved (2), holed conical (3) and possible transverse sections of previous type bodies (4). Examining possible terrestrial analogues, such microstructures are similar to terrestrial Dasycladales, Euglenoid, or giant filamentous cyanobacteria, rather than crystals. Please note that, the shapes are unambiguously identified by the large number of colored pixels contained.*

mineral present as precipitated cement within sediment pores [2], and hence an indicator of a local very acid environment and confined to the hardest structures.

Information regarding the dimensions of such structures, their shape and their layering, in relation to the sedimentary environment and their possible origin, are particularly important. Structures appear to be embedded within sediments of a quite aqueous environment and lack net contacts. Despite their random form and distribution, they show common features and appear as irregular aggregates, composed of globular and/or linear structures, affecting groups of laminae.

**115**

substances.

Magnetite and Phosphorous [2].

*Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

and curved filaments (**Figures 6** and **7**).

*5.1.4 Lenticular and conical/tubular structures*

*5.1.3 Filamentous microstructures*

structures [12, 13, 17].

The dimension of these aggregates, their unusual structure and distribution and the lacking of net contact with the host sediments, that'suggests that they are not transported/deposited elements, but that their formation was inside the sediment, after deposition, due to local cementation and/or grain rearrangement; conditions likely to be present during diagenesis and still existing in lake waters. In fact, chemical results indicate that Gale Crater sediments were strongly influenced by early, subaqueous diagenetic reactions that produced, and sometimes filled, a variety of pore types [49, 53]. Chemical and textural data indicate almost neutral lake water, while considerable local variations in pH [52]; so, they may suggest micro-environments and related microstructures generated by microbial activity and/or to the presence of local organic material. In addition, at the Mojave target site, traces of thiophene were found by the NASA scientific team, one of the main elements of kerogen; an organic compound that may be related to bacterial metabolism associated with terrestrial microbialites and, commonly, used as one of the main criteria to assess the biogenicity of putative Archean stromatolites [54, 56]. Particularly worthy of attention, both internally and externally, terrestrial stromatolites and Martian samples, both show elongated

Occurrence of filamentous structures, detectable by a different color and tone

MAHLI images taken at Sol 869 show that the lenticular lozenge-shaped "rice grains" observed on brushed surfaces at Sols 809 and 880 (Mojave target), not only occur "on the surface" as harder and whitish structure, but massively affect the entire outcrop, covering about 50% of the lithological mass. Previously, these structures have been interpreted as mineral deposits, e.g. of Gypsum or Jarosite (NASA reports), but subsequently, due to the lack of sufficient amount of crystal, they were interpreted as pseudo-morphic crystals originating from amorphous

In particular, the mineralogical composition of Mojave 2 (Sol 880) shows, in respect to the previous investigated rocks, a variation in mineral composition, exhibiting significant amounts of amorphous material (54%) and minor amount of Plagioclase (24%), Magnetite (4%), Hematite (4%), Jarosite (4%), Phyllosilicates (5%) and Fluorapatite (5%). Such data paradoxically suggest the coexistence of both oxidising (Hematite) and reducing (Magnetite) environments, as well as acidic (Jarosite) and neutral (Fluorapatite) components. Chemical data of this sample suggests the following composition: SiO2 (49%), FeO (16%), MgO (4%) CaO (4%) and Al2O3 (11%), together with other minor components, including

variation, normally appear to be formed by septate bodies having transversal dimensions of 0.05–0.3 mm (**Figures 6** and **7**). These structures are more evident on amplified/slightly blurred images of Martian sediments and on clean/abraded surfaces. Occasionally, they are more resistant and in relief, conditioning the shape of the laminar surface and their mutual contacts (**Figure 7**). They were observed, both as single features as well as intertwined structures and cover the rock surface resulting in a "woven" texture. Similar settings (**Figure 6**, frame G) have been investigated in previous work and interpreted, by visual and numerical approaches on a consistent number of terrestrial sampling analogues, as microbial/stromatolitic

## *Life on Mars: Clues, Evidence or Proof? DOI: http://dx.doi.org/10.5772/intechopen.95531*

The dimension of these aggregates, their unusual structure and distribution and the lacking of net contact with the host sediments, that'suggests that they are not transported/deposited elements, but that their formation was inside the sediment, after deposition, due to local cementation and/or grain rearrangement; conditions likely to be present during diagenesis and still existing in lake waters. In fact, chemical results indicate that Gale Crater sediments were strongly influenced by early, subaqueous diagenetic reactions that produced, and sometimes filled, a variety of pore types [49, 53]. Chemical and textural data indicate almost neutral lake water, while considerable local variations in pH [52]; so, they may suggest micro-environments and related microstructures generated by microbial activity and/or to the presence of local organic material. In addition, at the Mojave target site, traces of thiophene were found by the NASA scientific team, one of the main elements of kerogen; an organic compound that may be related to bacterial metabolism associated with terrestrial microbialites and, commonly, used as one of the main criteria to assess the biogenicity of putative Archean stromatolites [54, 56]. Particularly worthy of attention, both internally and externally, terrestrial stromatolites and Martian samples, both show elongated and curved filaments (**Figures 6** and **7**).
