**6. Discussion**

The first presence of organic matter on the Red Planet was revealed, even if initially misunderstood, by the Viking's pyrolysis gas chromatography–mass

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

spectrometry (GC–MS) analysis of Martian regolith [64]. More recently, the presence of chloromethane and dichloromethane, as markers of organic matter on Mars, were confirmed by SAM on Curiosity [65]. Since the Viking landers, organic matter has been repeatedly detected in Martian meteorites [66]. Hence, Curiosity rover drilled into the three-billion-year-old mudstones from four areas in Gale Crater and especially at Mojave and Cumberland sites, revealing many organic compounds, including thiophenic, aromatic, and aliphatic compounds, that were released at temperatures from 500° to 820°C [67], and reported in **Table 1**. The variety of different carbon-containing compounds provides evidence of possible macromolecules in the Martian regolith. Interpreting their presence, we can recall the kerogens observed on Mars: they are a type of organic molecule that can be easily associated with life (stromatolites), but, viceversa, it is also present in carbonrich meteorites, in interplanetary dust particles, and in igneous rocks, where life is not present. Nevertheless, the thiophenes observed on Mars, should be strongly suggestive of life [68], being easily explained as a result of biologically related sulfur

Moreover, it has been suggested that biominerals could be important indicators of life and thus could play an important role in the search for past or present life on Mars as on Earth [58, 69, 70]. Organic components themselves (Kerogene and Tiophene) are often associated with biominerals and are believed to play crucial roles in both pre-biotic and biotic reactions. They have been found in the fossil record that date back to the Precambrian and were used on Earth as evidence of the

On Mars, and in particular at Mojave targets, morphological observations of dendritic, nodular and laminated, harder structures (and complex organics, as well biominerals occurrence), may suggest a common origin, and may represent possible developmental stages of a single entity. Their variable dimensions, scattered distribution, and uncommon shape, show the same morphology as terrestrial microbialites. In this frame, noteworthy are the small nodular and encrusting microbialites, which are found in a wide range of lacustrine environments and in thin laminated mudstone, and they have been attributed to moderate wave agitation [71]; convincing parallels being visible, in the lake stromatolites of the West Germany lower Permian (Lauterecken Formation); as well as examples of stromatolites in nodular settings, forming larger cemented complexes known in current alkaline (pH > 9)

In this context, the irregular shapes assumed by the harder structures containing complex organics and biominerals most likely represent a results of bacterial or microalgae extracellular polymeric substances, according to an organic mineraliza-

The spatial development of stromatolites is important in interpreting their eventual structures. Hence, the basic structure of microbialitic sediments are essentially laminar (in plane), nodular (balls or lumps) and/or elongated (linear). These structures can also merge, respectively resulting in stromatolites, thrombolites, dendrolites and with ever-larger combinations providing all the typical known morphologies. The observed structures and morphologies, shown in **Figures 4**–**11** and all of those described to date in various studies, are all typical of

In general, the complexity and distinctiveness of biological structures increase with size and degree of biological evolution. There is still controversy on Earth regarding the biogenicity of some primordial microscopic structures and specialists attempt to solve these problems using instrumental insights and further laboratory investigations. These problems are generally related to the presence of possible very ancient microbial structures, having micrometric or sub-micrometric dimensions.

incorporation into organic matter during early diagenesis.

biogenicity of Archean stromatolites [56].

fresh lakes (Salda Lake, Turkey).

microbialitic world.

tion process present during diagenesis.

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

spectrometry (GC–MS) analysis of Martian regolith [64]. More recently, the presence of chloromethane and dichloromethane, as markers of organic matter on Mars, were confirmed by SAM on Curiosity [65]. Since the Viking landers, organic matter has been repeatedly detected in Martian meteorites [66]. Hence, Curiosity rover drilled into the three-billion-year-old mudstones from four areas in Gale Crater and especially at Mojave and Cumberland sites, revealing many organic compounds, including thiophenic, aromatic, and aliphatic compounds, that were released at temperatures from 500° to 820°C [67], and reported in **Table 1**. The variety of different carbon-containing compounds provides evidence of possible macromolecules in the Martian regolith. Interpreting their presence, we can recall the kerogens observed on Mars: they are a type of organic molecule that can be easily associated with life (stromatolites), but, viceversa, it is also present in carbonrich meteorites, in interplanetary dust particles, and in igneous rocks, where life is not present. Nevertheless, the thiophenes observed on Mars, should be strongly suggestive of life [68], being easily explained as a result of biologically related sulfur incorporation into organic matter during early diagenesis.

Moreover, it has been suggested that biominerals could be important indicators of life and thus could play an important role in the search for past or present life on Mars as on Earth [58, 69, 70]. Organic components themselves (Kerogene and Tiophene) are often associated with biominerals and are believed to play crucial roles in both pre-biotic and biotic reactions. They have been found in the fossil record that date back to the Precambrian and were used on Earth as evidence of the biogenicity of Archean stromatolites [56].

On Mars, and in particular at Mojave targets, morphological observations of dendritic, nodular and laminated, harder structures (and complex organics, as well biominerals occurrence), may suggest a common origin, and may represent possible developmental stages of a single entity. Their variable dimensions, scattered distribution, and uncommon shape, show the same morphology as terrestrial microbialites. In this frame, noteworthy are the small nodular and encrusting microbialites, which are found in a wide range of lacustrine environments and in thin laminated mudstone, and they have been attributed to moderate wave agitation [71]; convincing parallels being visible, in the lake stromatolites of the West Germany lower Permian (Lauterecken Formation); as well as examples of stromatolites in nodular settings, forming larger cemented complexes known in current alkaline (pH > 9) fresh lakes (Salda Lake, Turkey).

In this context, the irregular shapes assumed by the harder structures containing complex organics and biominerals most likely represent a results of bacterial or microalgae extracellular polymeric substances, according to an organic mineralization process present during diagenesis.

The spatial development of stromatolites is important in interpreting their eventual structures. Hence, the basic structure of microbialitic sediments are essentially laminar (in plane), nodular (balls or lumps) and/or elongated (linear). These structures can also merge, respectively resulting in stromatolites, thrombolites, dendrolites and with ever-larger combinations providing all the typical known morphologies. The observed structures and morphologies, shown in **Figures 4**–**11** and all of those described to date in various studies, are all typical of microbialitic world.

In general, the complexity and distinctiveness of biological structures increase with size and degree of biological evolution. There is still controversy on Earth regarding the biogenicity of some primordial microscopic structures and specialists attempt to solve these problems using instrumental insights and further laboratory investigations. These problems are generally related to the presence of possible very ancient microbial structures, having micrometric or sub-micrometric dimensions.

Indeed, microfossils, with a size of hundreds of microns, are more complex and distinctive, and on Earth other investigations are usually not necessary to recognize their biogenic nature.

In terms of "relevance for morphological recognition of biogenic structures", three domains could be distinguished: microbes, microfossils and fossils. Although doubts have often been expressed about the visual unambiguity of Martian microstructures, the described morphologies here described and related to putative "microalgae" should be considered unambiguous. In fact, the Mahli images that we have analyzed most frequently have pixels in the range 20–30 microns. For example, **Figure 9** (taken at Sol 880) which contain the lozenge-shaped bodies and the "cornucopia", have a pixel dimension of about 25 microns whereas the analyzed objects have millimetric or submillimetric dimensions and contain hundreds of colored pixels. As consequence, a single septate partition of the elongated structure shown in **Figure 9** (frame 1), having a dimension of about 0.1 mm, contains more than 16 colored pixels, which enables the septate structures to be unambigously observed.

Such filamentous segmented structures, having a cross section of 0.09–0.30 mm, are common in Martian sediments and have been described in previous papers [16, 72, 73]. In general, we can state that septate filament-like structures are frequent in terrestrial algal-like biota and that the Martian structures, that we have highlighted, are morphologically similar to a wide range of terrestrial counterparts (i.e., Epimastopora green alga; **Figure 14**).

The fossil record of septate bodies and the filaments are abundant, and are mainly characteristic of three big groups, i.e. Oscillatoriopsis, Megathrix, and those phosphatized tubular fossils (**Figure 15**) in the Ediacaran Weng'an Biota [74]. Oscillatoriopsis is characterized by unbranched, unsheathed, uniserate cellular trichome. The cells are uniform in length and diameter within the same trichome with no constrictions at the cell boundaries. Butterfield [75] recognized four species of Oscillatoriopsis according to their diameter, i.e., O. vermiformis Schopf, 1968, 1–3 μm; *O. obtusa* Schopf, 1968, 3–8 μm; O. amadeus Schopf and Blacic, 1971, 8–14 μm and O. longa Timofeev and Hermann, 1979, 14–25 μm.

Megathrix, however, are tubular microfossils typically less than 100 μm wide and several hundred μm long. These tubes, rarely branched, are characterized by evenly spaced transverse cross-walls which are complete or incomplete. Complete cross-walls are corrugated or flat and most are regularly intercalated with incomplete cross-walls. Incomplete cross-walls are flatter or less strongly corrugated than the complete examples and they have central perforations typically of similar size within the same specimen, although the perforation size may vary between specimens. Liu et al. [74] described five species of tubular microfossils from the Ediacaran Doushantuo Formation at Weng'an, Guizhou Province, South China. They also have complete and incomplete cross-walls [76]. However, the diameter of the Doushantuo species (mostly 100 μm – 250 μm in diameter) is much greater than Megathrix longus Yin L. and they all have flat rather than corrugated cross-walls. Of the five Doushantuo species, Ramitubus increscens Liu P. [74] and *Ramitubus decrescens* Liu P. [74] are both characterized by regularly dichotomous branching and rare incomplete cross-walls and by tetragonal tubes while *Crassitubus costatus* Liu P. [74] by a curved cylindrical tube with a longitudinal ridge, while *Quadratitubus orbigoniatus* Xue Y. [77] is characterized by a ridge. Finally, *Sinocyclocyclicus guizhouensis* Xue Y. [77] is most similar to *Megathrix longus* Yin L. except the former has greater diameter and flat cross-walls [76, 77]. We cannot be certain whether the septate filaments have corrugated or flat cross-walls but some ring-shaped (R) in **Figures 8** and **9** may represent central perforations on the cross walls; and very curved (VC) in the same figure have short incomplete walls, all supporting a resemblance to *Megathrix longus* Yin L.. The cornucopia-like

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**Figure 14.**

*structures.*

structures may represent oblique sections of tubular fossils with septate filaments such as present in *Megathrix longus* Yin L. or *Sinocyclocyclicus guizhouensis* Xue Y.

*Septate filament-like structures are biological "in principle" on Earth given a large number of algal structures having similar shape but different dimensions. On the left, three examples of different biota. Frames on the right represent Martian samples of similar structures. Right on the top (A), an enlarged cutting of Sol 880 image showing hard filament, in relief and septate. Frame B represent a reproduction of filamentous structure described on Figure 6, on frames H and I. Frame C is a ChemCam (CR0\_631854670PRC\_ F0781160CCAM03640L1) image catting showing some septate filaments, resembling intertwined filaments of spherules. In D similar structures observed in previous works and compared to some stromatolite similar* 

Moreover, morphometric investigations suggest a PCA and fractal dimensions of the "rice grains" with an affinity far from the mineral deposits studied such as gypsum, jarosite, and feldspar phenocrysts. In effect, phenocrysts are euhedral and angular whereas many of the Martian deposits are fusiform and exhibit a degree

[77] with possibly cyanobacteria affinity (**Figure 15**).

*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 14.**

*Septate filament-like structures are biological "in principle" on Earth given a large number of algal structures having similar shape but different dimensions. On the left, three examples of different biota. Frames on the right represent Martian samples of similar structures. Right on the top (A), an enlarged cutting of Sol 880 image showing hard filament, in relief and septate. Frame B represent a reproduction of filamentous structure described on Figure 6, on frames H and I. Frame C is a ChemCam (CR0\_631854670PRC\_ F0781160CCAM03640L1) image catting showing some septate filaments, resembling intertwined filaments of spherules. In D similar structures observed in previous works and compared to some stromatolite similar structures.*

structures may represent oblique sections of tubular fossils with septate filaments such as present in *Megathrix longus* Yin L. or *Sinocyclocyclicus guizhouensis* Xue Y. [77] with possibly cyanobacteria affinity (**Figure 15**).

Moreover, morphometric investigations suggest a PCA and fractal dimensions of the "rice grains" with an affinity far from the mineral deposits studied such as gypsum, jarosite, and feldspar phenocrysts. In effect, phenocrysts are euhedral and angular whereas many of the Martian deposits are fusiform and exhibit a degree

#### **Figure 15.**

*Microphotographs of a set of tubular septate-likes bodies thin sections, comparable to Martian samples. Frames A and B:* Oscillatoriopsis longa *Timofeev and Hermann, 1979; scale bars are 50* μ*m. Frames C-E:*  Megathrix longus *Yin L. from the lower Yurtus and lower Yanjiahe formations; scale bars are 100* μ*m. Frame F: 1.* Ramitubus increscens *Liu P., 2008 (scale bar is 200* μ*m); 2.* Ramitubus decrescens *Liu P., 2008 (scale bar is 200* μ*m); 3.* Sinocyclocyclicus guizhouensis *Xue Y., 1992 (scale bar is 100* μ*m); 4.* Quadratitubus orbigoniatus *Xue Y., 1992 (scale bar is 100* μ*m); 5.* Crassitubus costatus *Liu P., 2008 (scale bar is 100* μ*m); 6.* Yangtzitubus semiteres *Liu P., 2008 (This one is silicified and also from Ediacaran Doishantuo Formation; scale bar is 50* μ*m).*

of curvature. However, some gypsum and jarosite crystals exhibit a more fusiform shape but only a small proportion exhibited a degree of curvature which itself is regarded as a microbial biosignature [73].

Morphometric comparisons of "rice grains" with Euglena and Dasycladales have also been investigated, due to their morphological affinity. The fossil record of Euglena, however is rare [78–80] and only a fossil, called Moyenia, has been recorded from Late Ordovician non-marine deposits. This record was suggested by

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**Figure 16.**

*Structural features of Euglenae (from Loeblich and Tappan [81]) in comparison to the "rice grain" (A,B). "Rice grain" show curved (c) and very curved (vc) structures with holed transversal sections (t). 1–5 -*  Cleithronetrum cancellatum *Loeblich and Tappan, 1979 1, showing smooth distal portion of process, Scale bar 10* μ*m; 2, same specimen, showing slightly asymmetrical fusiform shape, Scale bar 30* μ*m; 3, nearly symmetrical lozenge-shaped outline, Scale bar 20* μ*m; 4, enlargement of surface of specimen of Figure 2, showing longitudinal sinuous and anastomosing ridges that bear tiny grana, Scale bar 10* μ*m; 5; scanning electron microscope photograph, showing partial or complete bridges between and perpendicular to longitudinal ridges and deep pits separating the bridges, Scale bar 5* μ*m. All from the Mountain Lake Member of the Bromide Formation of Oklahoma. 6,7 -* Eupoikilofusa striata *Staplin, Jansonius and Pocock n. comb. 6, holotype, blunt-tipped polar process that lacks the ridges found on median area of vesicle, Scale bar 20* μ*m; 7, overall view of holotype, showing longitudinal ridges, Scale bar 20* μ*m. From the Middle Ordovician, Trenton Formation, Anticosti Island, Canada. 8,9 -* Eupoikilofusa ctenista *Loeblich and Tappan, 1979. 8, holotype, enlargement to show nature and distribution of ridges on vesicle, Scale bar 20* μ*m; 9, lesser magnification of same, showing pointed processes that lack the ridges found on the vesicle, Scale bar 20* μ*m. From the Sylvan Shale of Oklahoma,*  Eupoikilofusa platynetrella *Loeblich and Tappan, 1979, holotype, showing slightly asymmetrical vesicle and distribution of vesicle ribs, Scale bar 20* μ*m. From the Sylvan Shale of Oklahoma. 11, 12-*Eupoikilofusa anolota *Loeblich and Tappan, 1979. 11, holotype, showing relatively broad and low discontinuous ridges, Scale bar 20* μ*m; 12, enlargement of surface to show wall sculpture, Scale bar 10* μ*m. From the Sylvan Shale of Oklahoma, 13,14 -* Eupoikilofusa parvuligranosa *Loeblich and Tappan, 1979. 13, holotype, nearly symmetrical fusiform vesicle with ridges that die out toward polar processes, Scale bar 20* μ*m; 14, enlargement of holotype to show sinuous ridges and grana aligned in rows on vesicle, Scale bar 10* μ*m. From the Sylvan Shale of Oklahoma.*

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

#### **Figure 16.**

*Structural features of Euglenae (from Loeblich and Tappan [81]) in comparison to the "rice grain" (A,B). "Rice grain" show curved (c) and very curved (vc) structures with holed transversal sections (t). 1–5 -*  Cleithronetrum cancellatum *Loeblich and Tappan, 1979 1, showing smooth distal portion of process, Scale bar 10* μ*m; 2, same specimen, showing slightly asymmetrical fusiform shape, Scale bar 30* μ*m; 3, nearly symmetrical lozenge-shaped outline, Scale bar 20* μ*m; 4, enlargement of surface of specimen of Figure 2, showing longitudinal sinuous and anastomosing ridges that bear tiny grana, Scale bar 10* μ*m; 5; scanning electron microscope photograph, showing partial or complete bridges between and perpendicular to longitudinal ridges and deep pits separating the bridges, Scale bar 5* μ*m. All from the Mountain Lake Member of the Bromide Formation of Oklahoma. 6,7 -* Eupoikilofusa striata *Staplin, Jansonius and Pocock n. comb. 6, holotype, blunt-tipped polar process that lacks the ridges found on median area of vesicle, Scale bar 20* μ*m; 7, overall view of holotype, showing longitudinal ridges, Scale bar 20* μ*m. From the Middle Ordovician, Trenton Formation, Anticosti Island, Canada. 8,9 -* Eupoikilofusa ctenista *Loeblich and Tappan, 1979. 8, holotype, enlargement to show nature and distribution of ridges on vesicle, Scale bar 20* μ*m; 9, lesser magnification of same, showing pointed processes that lack the ridges found on the vesicle, Scale bar 20* μ*m. From the Sylvan Shale of Oklahoma,*  Eupoikilofusa platynetrella *Loeblich and Tappan, 1979, holotype, showing slightly asymmetrical vesicle and distribution of vesicle ribs, Scale bar 20* μ*m. From the Sylvan Shale of Oklahoma. 11, 12-*Eupoikilofusa anolota *Loeblich and Tappan, 1979. 11, holotype, showing relatively broad and low discontinuous ridges, Scale bar 20* μ*m; 12, enlargement of surface to show wall sculpture, Scale bar 10* μ*m. From the Sylvan Shale of Oklahoma, 13,14 -* Eupoikilofusa parvuligranosa *Loeblich and Tappan, 1979. 13, holotype, nearly symmetrical fusiform vesicle with ridges that die out toward polar processes, Scale bar 20* μ*m; 14, enlargement of holotype to show sinuous ridges and grana aligned in rows on vesicle, Scale bar 10* μ*m. From the Sylvan Shale of Oklahoma.*

Colbath & Grenfell to be a possible fossil pellicle (cell wall) of a euglenid, based on their surface morphology, whereby the spiral pattern of ridges on the pellicle resembles that of some photoautotrophic euglenids in Monomorphina Mereschkowsky, 1877 [81]. **Figure 6** is particularly interesting and the cone present could easily be accepted as a fossil but given its incomplete preservation, it could be similar to a portion of Cloudina, a small shell fossil, or an example of other conotubular fossils (**Figure 16**). We emphasise, however, that the degree of variation in profile, width and shape and the degree of curvature of the profiles, both criteria highlighted by Williams [73] with consistency in width and curvature, are indicative of biogenicity and fractal analysis clearly confirms that the "rice grains" cannot be identified with mineral abiological structure as the gypsum, a result with a high statistical significance (p < 0.01).

Nevertheless, our conclusion in this paper concerning the analyzed Martian microstructures is not that they can be identified with the terrestrial species described but that the characteristics of shape and degree of complexity, make it probable that on Mars, 2.2 billion years ago, there were complex life forms, analogous to terrestrial eukaryotic cells. From a biological point of view, it is not unlikely that similar forms of life, with so many structural similarities, have developed independently on two different planets.

Results presented in this article can easily be interpreted as a phenomenon of evolutionary convergence, a phenomenon which is extremely widespread in terrestrial life forms. We can recall mammals and octopuses having camera-like eyes with an iris, a lens and a retina or the wings of bats and birds or the shape of sharks and dolphins: analogous environments producing the "same" shapes and structures without any evolutionary linkage. There no any problem for what concerns the time and the environment, on Earth, and, respectively, on Mars. Age of 2.2 billion years ago on Mars it is the same age in which complex, eukaryotic, cells, appeared on Earth, so there is no any problem for the time that could be need on Mars to produce those type of cells. No any problem, also, for the environment: the Earth aging 2.2–2.5 Gy ago is the one at the time of the oxygen crisis and of the "snowball Earth" [82], an anoxic and cold Earth as Mars of that age.
